Viable Alternatives for Effluent handling & disposal for Oilfield production operations

- K.R.Rao and S.N. Singh, ONGC-Ankleshwar

Introduction :

Oilfield effluents produced during operations (other than drilling & workover) consist mostly of saline water containing

emulsified oil particles (Patel C., 2004) – either in physical or chemical emulsion forms, fine colloidal particles of sand,

metal and chemicals, as well as phenolics and phenolic acids released by crude oil and above all traces of chemicals

used in the oil drilling, workover & activation process. The raw effluent characteristics generally vary in limits as

indicated in Table-I. As a comparison, treated effluent standards, as applicable to Indian oilfields for disposal are also

presented. Where the parameters exceed the upper limits shown, these effluents need to be identified for specific

treatment.

In deference to the effluent generated in oilfield operations, effluents generated during drilling include drill

cuttings etc. whereas workover operations lead to production of chemical containing saline effluents with varied

properties (Eugene F.B., 2005). Treatment of effluents for drilling & workover being specific to the type of effluent

generated, the present study has been aimed at analyzing the requirements for effluents generated during production

operations alone. Treatment of the effluent depends on a variety of factors, the most important ones amongst these

being oilfield location, collection methodology/ source, disposal mechanism, applicable legislation/ norms, quantity of

effluent, quality stipulations, end use philosophy and cost of treatment and disposal/ reuse. In most cases, the element

of cost is the major controlling factor. In most cases, re-use of the effluent is the most sought for option (Marselik J.

et.al. 2002). However, necessity requires disposal, when quantities become larger than reusable quanta, and it is at this

juncture the viable options for treatment & disposal are looked at (Elliott M, 2003; Bhanujan K.V., 2006).

Effluent Generation in Crude Oil & Gas Separation Processes :

Crude oil and gas separation processes generate effluents from the following various points (both offshore and

onshore). Segregation is carried out to accord pre-treatment to the effluent to make it suitable for mingling with the

mainstream. Figure-1 below indicates the generalized process of crude oil and gas separation and points of generation

of the effluents.(Bradley H.B., 1992).

a) Individual well line sampling points : Indicated by P1 in Fig.1, the drainage from the lines flows to the oily

water system (OWS). There is an intermingling with the floor washing, at times, and storm water during

monsoon. The quantities are small and infrequent.

b) Water drained from 3-phase separators : Indicated by P2 in the figure, this accounts for free water drainage

from the separator where the water and oil clearly separate out. It is routed directly to the Effluent storage

tank.

c) Water recovered from Heater-treater (or Emulsion treater – please refer Figure-2) : Indicated as P3, this is the

major quantity obtained by chemically and thermally breaking down the oil-water emulsion and purifying the

oil further by passing it through and electrical chamber where small droplets of water also separate out (Sams

G.W. et.al., 1999). It is also routed to the Effluent storage tank.

d) Water drained from Storage tanks : Rarely required to be done as direct water, P4 is usually recovered by

recycling tank bottoms through the Heater-treater (or Emulsion treater). In cases where large quantities of

water collect, direct free draining is done to the OWS.

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Apart from the above, effluent is also generated by a variety of other sources, to name a few :

e) Floor washings of oil pump house, compressor plants etc. : This is a marginal service water load and is

considered a storm water run-off. It sometimes goes to the OWS.

f) Fire water used during fire drills : This is also contaminated with oil to a certain extent and is led to the OWS.

g) Chemical handling and solution making e.g. demulsifier : This is a concentrated source and is usually

collected separately or otherwise led to the OWS or Effluent storage tanks.

h) Cooling water blow down from Cooling towers where recirculating cooling water is used e.g. in Gas

Compressors : The quantity is large and contains chemicals added to the cooling tower as well as iron picked

up from the Heat exchangers. This is treated separately before adding to the Storm water drain.

i) Rain water : This is the major contributor of Storm water and is usually not treated. It is led outside the

process premises through a large channel designed suitably to take the maximum rain water load to avoid

flooding within the premises.

j) Sanitary sewage : This comprises water run off from toilets, bathrooms, washbasins etc. It is usually led to a

separate Septic tank or Sewage treatment unit and not mixed with the other streams.

Segregation of Effluent streams :

The various streams produced with the locations have been presented above. Segregation, pre-treatment, treatment, re-

use or disposal all depend upon the factors as mentioned above viz. :

Location – onshore or offshore (Avinash D, 2003) •

•

•

•

•

•

•

•

Collection methodology/ source (Suresh B., 2005)

Disposal mechanism – surface/ sub-surface disposal .(Bradley H.B., 1992).

Applicable legislation/ norms (Kathuria V. et.al., 2000)

Quantity of effluent – volume and frequency/ rate (US EPA 625, 2002)

Quality stipulations – over and above legislation (Smith B., 1989)

End use philosophy (if any) – such as Water injection/ Air conditioning etc. (Bes-Pia A. et.al., 2002; Ekman

M., 2003)

Cost of treatment and disposal/ reuse (Volkman S., 2003; Feng X. et.al., 2004)

A graphical representation of the various routes available is presented at Figure-3. Segregation of the effluent streams is

done during design and construction of the plant/ unit or offshore platform. Table-II presents the various segregation

mechanisms available for the different factors as mentioned above, with names of the typical equipment such as Sump

Caisson (Frankiewicz T. et.al, 1999), API Separator, TPI Separator, DAF unit, Hydrocyclone (Navy/ Marines Process

Code, 1999), Sand/ Cartridge filters, used in such cases.

Quantization and Qualitative Analysis of Raw Effluents :

In order to deign, develop or optimize the effluent handling & treatment system, the type of effluents – quantity as well

as quality – need be estimated. It would be ideal if each stream can be identified, quantized and qualitatively analyzed.

However, this is not practicable and therefore broad sections are chosen and loads of quantity and quality estimated.

Procedures used for the same are as follows :

a) Sampling and analysis of available raw effluents : The physico-chemical characteristics of the available raw

effluents are determined analytically (REF), the major parameters being – pH, Oil & Grease, Total suspended

solids (TSS), Total dissolved solids (TDS), Chemical Oxygen Demand (COD), biochemical Oxygen Demand

(BOD), Phenolic substances, Sulphides etc.(Abouleish M. et.al, 2005; Method 4500-O, 1992)

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b) Quantization of raw effluent production from wells : This is done by using production profiles (Deokar V.G.

& Rao K.R., 2007). They depend upon reservoir characteristics, withdrawal rates, reservoir pressure balances

and lift mechanisms (draw down) used. Sand-wise data is compiled and profiles drawn up for Oil, gas &

effluents.

c) Rain water estimation : This is done on the basis of rainfall data available form the Metrological department

and the area covered. The maximum rainfall data during last 10 years is taken as the benchmark.

d) Service water run-offs : Estimated to be 2 M3/day for each pump house/ hose station with quality taken as that

of clean water.

e) Cooling Tower blow down : This is taken as 10% of the quantity of recirculating cooling water in the circuit.

Quality is identified by sampling and analysis as per (a) above.

f) Sanitary sewage : Sanitary sewage water is considered to be the entire potable water consumption which is

estimated on per head basis as approx. 100 litres/person/day (Manual of Naval Preventive Medicine, 2005).

With the different streams estimated, the summation as per the segregation indicated in Figure-3 is applied, and systems

designed for treatment, handling & disposal on the basis of this data.

Effluent Disposal Methods – Legislative & Other Requirements :

The entire design of the effluent handling system hinges on the mode of disposal, which is invariably dictated by the

following :

a) Geographical location and Topography : This is most important. Offshore disposals vary from onshore

land/ river disposal mechanisms. Also, space is at a premium in offshore operations. On land, collection of

effluent is possible.

b) Pollution control laws : Effluent disposal is covered under the Water Act, 1974 and Rules & regulations

made thereafter by the Ministry of Environment & Forests (MoEF) as well as the State Pollution Control

Boards (SPCBs). As per the legislative requirements, the operating company has to apply for a Consolidated

(Air/ Water/ Hazardous Waste) Consent to the SPCBs and obtain the same. The consent will present

stipulations which will have to be followed. In addition, monthly monitoring of environmental parameters and

annual Environmental Auditing has to be got done through SPCB approved agencies.

While applying for the consent, the effluent disposal mechanism, quality and quantity has to be

submitted to the SPCB and on approval, the same shall appear as a stipulation to be followed.

c) Environment Impact Assessment (EIA) and Public Concerns : EIA is carried out initially during pre-

design phase for projects involving costs of Rs.10 crore plus. Effluent disposal figures as a major issue in EIA.

Apart from the above, public concerns play an important role, particularly more so if the company is

ISO-14001 certified. Transportation and discharge of effluents is dictated by public opinion in numerous

cases. In case of pipeline transport of effluent, the right of use (ROU) for laying the pipeline is again governed

by Public opinion.

d) Reuse/ Re-injection option : These are technical options and are guided by the reservoir requirement

(Harding T. G. et.al, 2002). Effluent quality adjustment is a key factor. Some of the options in vogue are :

i) Re-injection into sub-surface : In this case, there are again two types :

Re-injection to same strata from where effluent is produced : Quantity to be re-injected is of

consideration here. The quality need be adjusted by filtration alone.

Re-injection into different strata from that which produced the effluent : In this case, apart from

filtration, adjustment for salinity by adding de-oxygenated fresh water) is also required.

Quantity is also a check.

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ii) Reuse for Steam generation : This is a very limited requirement. It is used where steam is required

such as in the case of production of tar sands using Steam Assisted Gravity Drainage (SAGD). The

water is required to be brought to boiler feed-water quality level, using either :

Ion exchange/ softening (Brown C.J. et.al, 2002)

Dealkylation/ Demineralization (Smith B. et.al., 2000)

Electro-deionization (Ma H. et.al., 2006)

Pulse Energy Transformation (PET ) technology (Begell W. et.al., 2003)

Pervaporation followed by deminerlization / ultrafiltration (Garcíaa V. et.al., 2006)

iii) Reuse for process/ potable consumption : In this context, high purity filtration techniques are

required to be used such as : Reverse Osmosis (RO), Microfiltration (MF), Ultrafiltration (UF),

Nanofiltration (NF), Activated carbon adsorption, Carbonate freezing, Electrodialysis (ED),

Electrolytic recovery (ref. USEPA 821, 2002). For potable use, the mineral salt content will be

required to be adjusted by chemical addition.

In each of the reuse/ re-injection option, quantity and quality both are deterministic. Excess quantity of

effluent being available may be required to be disposed off. Also, effluent rejects from Reverse Osmosis etc.

need consideration from disposal point of view.

To exemplify the above, few of the different types of disposal mechanisms are shown diagrammatically in Figure-4, for

given constraints and requirements as indicated.

Effluent Treatment Techniques :

Effluent treatment is invariably a process determined by the input quantity, quality and type of effluent which is

required to be disposed off/ reused in the manner most suitably designed to assure that all constraining parameters are

met with. The processes are designed to meet the pollutant load types and end result required. Table-III gives a

simplified version of the techniques adopted, though no standard process is defined, and every effluent requires to be

considered on case-to-case basis for treatment.

Case Study-I : Effluent handling at Lakwa-Lakhmani oilfields, Assam :

The Lakwa-Lakhmani oilfield of Assam is one of the oldest and is operating with average water content in the well

fluids at about 60-90% (Nischal T.H. et.al, 2007). Effluent quantity is large. However, the effluent is not very saline

and requires hardly any treatment for dissolved solids control. Other constraints such as long distances over which

effluents have to travel, excess effluent disposal over and above the injection quantity and oil shock load handling

dictate the terms for the effluent handling mechanism. The raw effluent, treated effluent for water injection and disposal

lines are as schematically indicated at Figuire-5.

The effluent is generated from 10 different installations and piped to the inlet of ETP-I. There are 2 effluent

treatment plants with following features :

• ETP-I : Old plant of capacity 6000 M3/day based on free oil separation in Wash tank, Surge pond and

API separators followed by physico-chemical treatment with Lime & Alum and settling of chemical

sludge in clarifier.

• ETP-II : New plant of 5000 M2/day capacity based on free oil separation in Wash tank & TPI, followed

by physicochemical Alum-polyelectrolyte treatment with separation of chemical sludge in Dissolved Air

flotation unit, followed by biological treatment in Trickling filters and finally polishing in Sand and

carbon filters.

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ETP-II was constructed in 2000 and was built to substitute ETP-I, as the old plant was aging. The ETP-I had the

advantage of long residence time and a large Surge pond for Free oil separation. ETP-II was found to be useful as it had

the biological treatment facility. In order to obtain the nest performance, both plants were configured to operate either

in parallel or in series and ETP-I refurbished to the extent required..

A typical raw effluent pattern of the oil and grease content and TSS measured over a period of one year is

presented, with the typical outflow characteristics from ETP-I and ETP-II separately, when operated separately and

both combined when operated in series is presented at Figures 6. From the data presented, it is visible that shock

loadings of oil from the GGSs prevail at the ETPs. As the residence time of ETP-I was larger, the oil shock load could

only be handled at ETP-I and ETP-II was found to be most suitable to take care of physico-chemical treatment coupled

with biological treatment. Modifications were carried out in both plants and the final disposal/ reuse mechanism

evolved is as under :

• For water injection, effluent from the outlet of DAF unit of ETP-II was found to be most suitable.

• Only excess effluent required to be disposed of to the river was taken up for biological treatment & filtration

from outlet of ETP-II.

• Water injection at Lakwa requires micro-filtration and addition of chemicals. About 2500 CuM/day was taken

up for water injection and the remaining disposed of in river.

Case study II : Effluent handling for remote oilfields of Ankleshwar Asset, Gujarat :

Remote oilfields of Ankleshwar Asset are situated in the northern corner of the Gandhar oilfield, on the other side of

Dadhar river. Figure-7 indicates the oilfields producing oil & gas in Area-IV of ONGC-Ankleshwar Asset. Being

remote and widespread, setting of centralized facilities works out to be a costlier option. Hence the system of

processing at the installations and direct piping of products to consumers is applicable here.

The effluents generated in these oilfields are separated out at the installations of Area-IV and processed crude

oil is sent to the refinery through pipelines, while gas is separated out, compressed (if required) and sent directly to

consumers. Effluent variations being large, local handling systems need to be versatile to deal with the variation (Mehta

S.D., 2005). Initial effluent loads were being disposed of by evaporation in flare pits. As the quantum of effluent

generation increased, Effluent Disposal (ED) wells were created and disposal as on date is done in these wells.

With the quantum leap that is expected to take place, it has been proposed to transfer the effluent through large

pipelines to the Effluent Treatment Plant at Central Processing Facilities (CPF) - Gandhar. A study was undertaken for

analyzing the technical constraints and the cost factors involved by taking up three variants, based on the geographic

locations and the quantities of effluent to be generated at each of these installations. Data concluded from the study is

presented in Table –IV.

From the data in Table-IV, it is evident that the best possible solution is follow being cost effective. Variant-I,

that is piping the entire effluent from the installations via a pipeline to CPF-Gandhar. Detailed calculations for the

pipeline have been done and it has been proposed to lay a 10” dia. Glass Reinforced Plastic pipeline (Salibi Z, 2001) to

transfer the effluent. As a stand-by recourse to leakage of the pipeline or other problem which may stall the transfer of

effluent, the storage of effluent as well as alternate means of disposal of part effluent to ED wells is also planned. The

capacity augmentation of the ETP at CPF-Gandhar is also being taken up parallely.

Case study III : Effluent handling at Central Tank Farm, Ankleshwar, Gujarat :

The entire quantity of effluent generated in the oilfields of Area-I (Ankleshwar, Sisodara, Motwan) and Area-II (Kim,

Kosamba) gets collected at Central Tank Farm (CTF), Ankleshwar. A total of approx. 4800 CuM/day effluent is

generated and water injection requirement is 1800 CuM/day. An older version ETP is operative at CTF-Ankleshwar in

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which, free oil is separated out in Wash tanks, physico-chemical separation of oil-water emulsion is done by adding

PAC and separating the oil in Surge ponds followed by API separators. The disposal of the extra effluent was being

done at the Narmada creek as shown by the blue line as shown in the diagram at Figure-9.

Effluent of the GIDC-Ankleshwar having been a problem in the past, wherein the Amalakhadi creek was

totally polluted by disposals (Labunska I. et.al., 1999), social activism with regard to effluent disposal in this region is

high. Following reports of frequent leakage of pipeline and changes in the water bodies over the years, a study was got

undertaken thorugh National Institute of Oceanography (NIO), Goa to find an appropriate location for the effluent

diffuser point and also to change the material of the pipeline to Glass Reinforced Plastic (GRP). Additionally, process

was undertaken to go in for a new ETP to handle 6000 CuM/day of effluent and make it suitable for marine disposal.

NIO, Goa submitted it’s report (Kadam A.N. et.al, 2005) and accordingly pipeline laying was undertaken. As

per NIO, the location determined by scientific evaluation was at a point in the Narmada estuary where the water depth

varies between 3.5 to 8 metres. Being CRZ location, this would require MoEF approval. Meanwhile, following the

decree awarded in the Tribunal on Environment and Human Rights delivered by Hon. Justice. Hosbet Suresh in

February 1999, a special purpose vehicle was set up. M/s Bharuch Eco Aqua Infrastructure Limited (BEAIL) is the

Special Purpose Vehicle set up for the purpose of implementing the effluent disposal project for the industrial estates of

Ankleshwar, Jhagadia and Panoli in the Bharuch district of Gujarat state. The project involves three components :-

• 60 MLD Waste water treatment Plant (CETP)

• 44 Kms. long On Shore Pipeline

• 10 kms. Off shore pipeline with diffuser in the Gulf of Cambay

Details of BEAIL disposal mechanism is also presented in Figure-9 (red line).

Clearances for estuarine disposal of effluents have not been given by MoEF in the recent past. Instead of

laying a separate pipeline to the sea, pressure from local NGOs was put on ONGC and GPCB. As a result, GPCB had

to resort to cutting of power to CTF-Ankleshwar for ONGC to either join CETP of BEAIL, seek alternative legal

disposal route or close down. As an alternative measure, wells in Ankleshwar field were developed for effluent disposal

and at present 23 wells are available for taking the liquid. The area is earmarked in the diagram at Figure-9.

Construction of new ETP at CTF-Ankleshwar is also is progress. BEAIL has indicated inability to take the

large quantity of ONGC effluent as on date. The two options available at this juncture are :

• Process the effluent for ED wells and dispose of in the wells – more ED wells to be developed with time

• Consider reuse/ recharge options for purifying water quality and making it suitable for agricultural or other

purposes.

Salinity of the effluent is high (around 13000 – 17000 ppm) for which reason, conventional membrane techniques may

prove costly.

Case study IV : Effluent handling at Hazira Gas Processing Complex, Gujarat :

The Hazira Gas Processing Complex of ONGC utilizes water for process, cooling, domestic as well as service water

requirements and delivers an equivalent quantity of effluent at different points. Contamination levels of the effluents

vary and therefore the first necessary part of the system is to segregate and group the effluents. Six units of effluent

treatment are available and treatment and handling in each case differs. The process system and effluent fall-out routes

are indicated in Figure-10. Table-V presents the different varieties of effluents, their generation points, characteristics

and handling & treatment provisions.

The streams delineated in the table were not clearly visible during the construction phase of the Hazira Gas

Processing Complex and there was much intermingling. Certain problems faced during the initial operation periods and

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the measures undertaken to resolve the issues are as deliberated below. Also, certain innovative measures to improve

performance of wastewater treatment & ecology of the area are recorded, as follows :

1. High temperature of Process waste stream : This was causing the lighter hydrocarbon fractions to release in the

drainage system itself. Also, Sulphate Reducing Bacteria (SRBs) were growing fast within the drain sections

before they could be taken up for treatment at the PWTPs. PWTP sump pump seals were failing regularly due to

high temperature.

The problem was located and found to be one of the most essential system that had been overlooked. The

steam condensate was being dumped along with process chemicals into the PWS. This was not only causing high

temperature in the PWS but, was also a colossal loss of treated water as Boiler feed water, which was required to

be recycled. Also, the steam drain traps were routed to the PWS causing similar problem.

As a first measure, systems were erected for steam condensate return to boilers. A header was put up and

vessels used which would get pressurized by steam and push the condensate back to boilers.

2. Frequent chocking of PWS and SCS drain lines : Specifically SCS drain lines were found to choke and on cleaning

manually, a black substance similar to that of boot-polish was found to cover the pipelines connecting the drains.

A dilute Hydrochloric acid wash in sequential steps was carried out and the drains cleared upto SCTP.

Recurrence of the black substance did not occur.

3. Cooling water blow down diverted to storm water channel : Initially, iron pick-up being high, large quantities of

cooling water blow down were effected. It was observed that the entire quantity entered the storm water channel as

the OWS was not extended up this point.

As a first measure, OWS was extended upto Side stream filters of Cooling towers. On study, it was found that

iron pick-up was high due to excessive Sulphuric acid dosing to maintain pH. System was changed over to

Alkaline SHMP+HEDP system and cycles of concentration increased. This reduced the load on the OWS. Also,

passivation was once again carried out and iron pick-up controlled.

4. Regular choking of Sanitary sewage : A typical phenomenon, this was found to be due to excessive dumping of

food wastes in the sewage system. A guard pit was constructed at the canteen drain and frequent cleaning ensured

to keep only fluids to pass through. System was found to falter on occasions and cleaning had to be resorted to

again.

5. Overloading of storm water drain during acid-alkali wash of resins of DM plant : The DM plant was found to use

Hydrochloric acid and Caustic lye to regenerate the resins. The spent wash water was collected in a sump and pH

neutralized invariably by adding alkali. After addition of alkali, the entire high TDS water was pumped to storm

water channel, through drains, overloading it.

As the pH of the water was low, an interconnection of the acidic stream with the spent caustic drain was made

thereby saving on acid at SCTP. It also helped add to dilution water and further completely reduced the load on

storm water drains in the area.

6. Huge quantity of water lost to storm water drain during backwashing of Raw water filters and also Sand choking

of storm water drains : This was arrested by commissioning the air blowers and backwashing filters in stages. A

channel was created to route the backwash water back to inlet sump, thereby saving large quantities of water,

reducing sand loss, preventing choking of storm drain canal and above all, improving the sand filter life.

7. Improper biological treatment of process waste : Shock loads of different chemicals were found to occur in the

PWS and as a result, equalization tank was getting overloaded. COD loads of TEG were found to be 8000 ppm per

ml of TEG and MDEA was found to give 6500 ppm per ml. a technique of seed-control by recycling sludge in

anoxic condition was tried out and first results obtained are presented at Figure-11. The approach was repeated at

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Lakwa and is part of design for ETP being constructed at CTF-Ankleshwar based on research data (Rao K.R.,

2004)

8. Aquaculture in treated wastewater : The guard pond of PWTP was found to be an ideal location for aquaculture –

fish farming. Additional floating type aerator was procured and with the help of Fisheries Department of Gujarat,

three types of fish – Rohu, Katla & Mrigel were grown. The fish farming continues even to this day.

Modern proposed techniques yet to be proven :

Other systems available in literature, which are yet to be proven are :

1. Downhole separation of wastewater : Efforts have been made to place surface produced water management

practices downhole to avoid some of the costs incurred from producing the underground water to the surface. It has

been observed that “pure” streams of hydrocarbon production can be achieved using this technique.

2. Adsorption of oil : A case of hydrocarbon adsorption product referred to as laponite that effectively removes oil

from emulsions is referred in lietrature. A similar product employs silicone as a demulsifying agent. Additionally,

Kuwait Petroleum Corporation recommends a product known as CAPS or Organoclay for produced water

purification.

3. Decentralized Concept of Wastewater Management : Here blocks are divided and pre-treatment of wastewater of

one block done to feed the next block or act as diluent for it’s effluent. The concept is fast catching on.

Wastewater Treatment and Water Management :

The concept of wastewater treatment is nowadays linked to water management, with the 4R-concept of Reuse, Recycle,

Recharge/ Renovate/ Recover and Reduce. Numerous techniques have been stipulated for the purpose and some of

these which are in vogue and are giving results are as follows :

1. Drip irrigation utilizing high salinity treated wastewater – In fact RO system rejects have also been used in

certain cases. A layer of salt is formed at the edge which is periodically removed out manually.

2. Reed bed purification - A reed bed is a natural filtration process used in conjunction with biological treatment

to further enhance the quality of effluent migrating into surrounding watercourse.

3. Arresting evaporation losses from large ponds – Numerous methods are available to cover the surface such as

Fatty alcohol covers, polyurethane foam sheets, polyurethane balls etc. Studies with pan evaporimeter have

been carried out at Hazira to determine the losses ( Rao K.R. et.al., 1989)

4. Reuse of boiler blowdown water to be conditioned and made as feed to Cooling water system – Losses of

Phosphates can be controlled in this manner, reducing chemical utilization. The temperature of the blowdown

water has to be reduced and can be used effectively as a heating medium for solution making.

5. Use of effluents for hydrotesting of pipelines : This has been tried out at Ankleshwar and requires refinement

for quality control and education of water reuse. Concepts that wastewater is bad quality water need to be set

aside.

6. Hot water flushing of pipelines using heater-treater water : This has been tried out at Lakwa in Assam. Care

needs to be taken. Equipment designs can be modified to adopt this technique.

Conclusion :

The concept of effluent as a quality of water – with ingredients that can be used has to be imbibed, instead of rejecting

it as wastewater. Viable alternatives for handling, disposal and reuse will always depend upon the availability of

resource and the ease of operations for disposing the unwanted material without creating legal/ socio-political issues.

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Acknowledgment :

The authors acknowledge the support and guidance of Sh. Chatar Singh, Executive Director – Asset Manager, ONGC-

Ankleshwar Asset for having provided the opportunity for presenting the subject paper. Also, acknowledgment is

placed on record for the help given by Sh. S.C. Upadhyay, Executive Director (Retd.), Sh. K. Anjenuyulu,

GGM(Prodn.), Sh. S. Prasad, GGM(Prodn.) (Retd.), Sh. B.B. Patel, DGM(Mech.) and Prof. Subrahmanyam.

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1996, URL : www.cpcb.nic.in/ Environmental_standards Eugene Furrow Brendan (2005) - "Analysis of Hydrocarbon removal methods for the management of oilfield

brines and produced waters" - MS Thesis - Texas A&M University, Houston, Texas, pp 65 Feng X. and Chu K.H. (2004) - "Cost Optimization of Industrial Wastewater Reuse Systems" - Process Safety

and Environmental Protection, Vol. 82, No. B3 Special issue: Clean Technology and Waste Minimization, pp 249-255 Frankiewicz Ted and Clemens Joe (1999) - "Solving problems with overboard water handling systems" - World

Oil, Vol. 220, No.1, pp.16-22 Garcíaa Verónica, Landaburu-Aguirrea Junkal, Pongracza Eva, Phillips Paul, Keiski Riitta (2006) – “Recycling

of organic solvents by pervaporation and micellar-enhanced ultrafiltration” – Desalination, Vol. 200, pp. 383–384 (Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy) Garland Emmanual (2003) - "Discharge of Produced Water: New Challenges in Europe" - SPE/EPA/DOE

Exploration and Production Environmental Conference, 10-12 March 2003, San Antonio, Texas, USA, pp.9 Harding T. G., Smith K. H, Norris B. (2002) – “Horizontal Water Disposal Well Performance in a High

Porosity and Permeability Reservoir” - Symposium and International Horizontal Well Technology Conference, 2002 SPE International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference, Calgary, Alberta, Canada, 4–7 November 2002, pp. 1-20 Kadam A.N., Mandalia A.V., Sarma R.V. and Sukumaran Soniya (2005) - "Comprehensive marine EIA for the

Release of ONGC effluent in Narmada estuary" - Report of National Institute of Oceanography, Aug 2005, pp.80 Kathuria V. and Sterner T. (2000) - "Monitoring and Enforcement : Is Two-Tier Regulation robust ? - A case

study of Ankleshwar, India" - Conference at Institute of Economic Growth, Delhi, September 19, 2000

9

Labunska I, Stephenson A., Bridgen K., Santillo D., Stringer R., Johnston P.A. and Ashton J.M. (1999) - " Organic and heavy metal contaminants in samples at three industrial estates in Gujarat, India" - Greenperace Research Labortatories, Technical note 05/99, Exeter 1999. Ma Hongzhu and Wang Bo (2006) - "Electrochemical pilot scale plant for oilfield produced wastewater by

metal/ carbon/ iron electrodes for injection" - Journal of Hazardous Materials, Vol.41, No.7, pp. 1475-1483 Manual of Naval Preventive Medicine(2005) : Chapter 7: Wastewater Treatment and Disposal, Ashore and

Afloat: Section II. Wastewater Treatment and Disposal Systems Ashore, Collective copyright © 1997-2005 The Virtual Naval Hospital Project. URL: http://www.vnh.org/ Marsalek, J, K Schaefer, K Exall, L. Brannen and B. Aidun. 2002. Water Reuse and Recycling. Canadian

Council of Ministers of the Environment, Winnipeg, Manitoba.CCME Linking Water Science to Policy Workshop Series. Report No. 3. pp 39 Mehta Shweta D. (2005) - "Making and breaking of water in crude oil emulsions" - MS Thesis, Texas A&M

University, Dec. 2005, pp. 78 Method 4500-O (1992), Standard Methods for the Examination of Water and Wastewater, APHA-AWWA-

WEF, 18th ed. Navy/ Marines Process Code (1999) - "Air sparged hydrocyclone (ASH) for treating wastewater" - Process

code SER-016-99, URL : www.p2library.nfere.navy.mil/P2_Opportunity_Handbook/ 9_1V_6.html Nischal T.H., Mitra S., Sujith Kumar R. and Nath S. (2007) - "Integrated and multidisciplinary approach arrests

production decline in mature Lakwa-Lakhmani field - A case study" - Presented at PETROTECH 2007, 7th International Oil & Gas Conference and Exhibition, Jan 15-19, 2007, New Delhi, India Patel Chirag (2004) - "Management of Produced water in Oil and Gas productions" - MS Thesis, Texas A&M

University, Houston, Texas, pp 85 Production Equipment (1996) - Baker Production Services, Reference document Rao K.R. (2004) - "Studies on "Seed-controlled" Activated Sludge Process" - Ph.D. Thesis, MS University,

Vadodara, India, Noiv. 2004, pp. 278 Rao K.R. and Madhav Kant (1989) - "Water Management at ONGC-Hazira" - Paper presented at Indian

Institute of Engineers, Ahmedabad, India, Dec 02, 1989, pp.25 Salibi Ziad (2001) – “Performance of reinforced thermosetting resin pipe systems in desalination applications: a

long-term solution to corrosion — The Arabian Gulf example” – Desalination, Vol.138, pp. 379–384 Sams Gary W. and Zaouk Moshen (1999) - "The practised art of emulsion resolution in electrostatic processes"

- AIChE Spring meeting, Houston, Texas, pp 9 Smith Bradley and Hyde Bill (2000) – “Short-Bed Demineralization: An Alternative to Electro-deionization” -

Presented at the Sixth International Conference on Cycle Chemistry in Fossil Plants (EPRI), Columbus, Ohio, June, 2000 pp. 6 Smith Brent (1989) - "BOD and COD sources and reduction strategies" - Internal communication, May 1i989,

pp.30 Suresh B. (2005) - "Public Private Partnership for Water and Wastewater Management" - CII Water Summit,

November 26, 2005, pp. 14 UFC 4-832-01N (2004) - “Unified facilities criteria (UFC) - Design: industrial and oily Wastewater control” -

U.S. ARMY CORPS OF ENGINEERS – Internal Communication US EPA 625 (2002) - "Treatment System Selection - US EPA Onsite Wastewater Treatment Systems Manual

EPA/625/R-00/008" - Feb. 2002, URL : www.epa.gov/nrmrl/pubs/625r00008/html/625R00008.htm USEPA 821 (2002) - "Pollution prevetion and practices" - Chapter 8, Development document for proposed

effluent limitation guidelines, USEPA 821-B-01-007, Jan. 2002, pp. 55 Volkman Sarah (2003) - "Sustainable Wastewater Treatment and Reuse in Urban Areas of the Developing

World" - Internal communication, MS Program, Michigan Technological University, April 2003, pp 18

10

TABLE – I : General Characteristics of Effluents released in Oilfield operations versus approved effluent disposal standards

Characteristics Units Lower limit Upper limit Physico-Chemical

pH - 4.0 10.5 Oil & grease ppm 3.6 14500 Total Suspended Solids ppm 3.3 1521 Total Dissolved Solids ppm 46 34000 Volatile Suspended Solids ppm 1.5 1506 Chemical Oxygen Demand ppm 1337 2709 Biochemical Oxygen Demand ppm Phenolic compounds ppm 0.001 0.409

Metals Aluminum ppm 0.20 2.00 Cadmium ppm 0.01 0.05 Chromium ppm 0.01 0.07 Copper ppm 0.01 2.20 Iron ppm 0.01 7.50 Lead ppm 0.01 0.53 Mercury ppb 0.01 2.77 Nickel ppm 0.01 0.04 Silver ppm 0.01 0.01 Zinc ppm 0.32 12.00

Data obtained from “Unified facilities criteria (UFC) - Design: industrial and oily Wastewater control” - U.S. ARMY CORPS OF ENGINEERS (2004)

PARAMETER S F URFACEAL

E UNIT OR S

DISPOS FOR MARIN

DISPOSAL5.5 – 9.0 5.5 – 9.0

Temperature eg.C d < 40 < 40 Colour Units 100 < < 100 Oil & Grease 0 10 ppm < 1 < Total Suspended Solids m 100 (TSS) pp < < 100

Total Dissolved Solids (TDS) m 100 pp < 2 Chemical Oxygen Dema(COD)

nd m 0 < 100 pp < 10

Biochemical Oxygen Demand (BOD) m 0 30 pp < 3 <

Phenolics ppm < 1 Sulphides ppm < 2.8 Ammonical Nitrogen m pp < 50 Data obtained from Environmental Sta – Efflu l & Gas Indu ry – CPCB

176(E), Aprindards ent – Oi st

– EPA Notification, GSR l 1996

pH

11

TABLE-II : Segregation of waste streams & treatment/ disposal philosophies for Offshore and Onshore locations

LOCATION : Well

Sampling

Water drained

Chemical

Effluent

Separators

Effluent

Storage

Effluent

Emulsion

Floor Process

Rain Sanitary

OFFSHORE Fluid from

point

from

Tanks

drained from 3-phase

drained from

Tanks

drained from

heaters

wash-ings

blow-downs water sewage

Direct to ProducedWater Storage

irect to ProducedWater Storage

irect to ProducedWater Storage

Systems

drain Watesystem

Watesystem

water drain

Sludge digestion

Sump Caisso

itioning skid

IGF/ DAF units Control System

system SuCaisso

Sump Sump Insea Into sea

Sub-surface Effluent Disposal wells

Reuse Process

ONSHORE Fluid from

point

from

Tanks

drained from 3-phase

drained from

Tanks

drained from

heaters

wash-ings

blow-downs water sewage

ProducedWater Storage

ProducedWater Storage

ProducedWater Storage

Systems

bucket Watesystem

Watesystem

water drain drain

Oil/ wateseparator Oil sk ming

Flocculation Control System

Tertiary Sand/ Cartridge filters

board disposal point - if required Odrain

Odrain

Odrain

surfac

with produwater

produced water Filtration and pressurized disposal

into Effluent disposal wells

Disposal/ Reinjection/

Reuse

Process Partly reused for re-injection, steam generation for SAGD etc.

Regular

D

D

Collection

Irregular Closed Closed drain Oily

r Oily

r

Storm Maceration/

Physical n

Chemical To

Produced Water cond-

Froth flocculation/ Hydrocyclone/

Treatment/

Tertiary Anaerobic

Surface mp n

Sump Caisson Sump Caisson Caisson Caisson

to

Disposal/ Reinjection/

Partly used for Air-conditioning cooling & toilet wash water service

LOCATION : Well

Sampling

Water drained

Chemical

Effluent

Separators

Effluent

Storage

Effluent

Emulsion

Floor Process

Rain Sanitary

Regular Direct to

Direct to

Direct to

Collection

Irregular Open Closed drain

Oily r

Oily r

Storm Sewage

Physical r Oil Water API/ TPI Separators im

Chemical Coagulation/ IGF/DAF unit/ Hydrocyclone

Treatment/

Surface As per approved pollution control

further treatment to be given in ETPs pen pen pen

Sub-e

Along

ced Along with

Soak pit

12

TABLE-III Effluent tre es ad pted the : atment techniqu o in

Oilfield production industry

Effluent Type

Pre-treatment

Primary treatment

Secondary treatment

Tertiary treatment

Disposal method

Free oil containing oilfield effluent (offshore)

Segregation Equalization

API/ TPI separation

Sump Caisson

Segregation Equalization

API/ TPI separation

Filtration ⇒ Pressure

Sand filters ⇒ Micron filters

Sub-surface disposal (ED wells)

Free oil containing oilfield effluent (onshore)

Segregation Equalization

API/ TPI separation

Surface disposal to estuary or reuse for gardening/ horticulture

Segregation Equalization

API/ TPI separation Chemical coagulation & flocculation – DAF units

Electrostatic demulsification Filtration ⇒ Pressure

Sand filters ⇒ Activated

carbon filters ⇒ Micron filters

Sub-surface disposal (ED wells)

Emulsified oil containing oilfield effluent

Segregation Equalization

API/ TPI separation Chemical coagulation & flocculation – DAF units

Biological treatment o Fixed film process –

Biotowers, Rotating Biological contactors

OR o Suspended film process –

Activated sludge process

Filtration ⇒ Pressure

Sand filters

Surface disposal to estuary or reuse for gardening/ horticulture

Chemical containing hydro-carbon bearing effluents

Segregation Equalization

API/ TPI separation Chemical coagulation & flocculation – DAF units

Biological treatment o Fixed film process –

Biotowers, Rotating Biological contactors

OR o Suspended film process –

Activated sludge process

Filtration ⇒ Pressure

Sand filters ⇒ Activated

carbon filters

Surface disposal or reuse for gardening/ horticulture

High sulphide containing effluent

Segregation Equalization

Wet Air Oxidation Electro-deionization Crystallization of Sodium Sulphide

Biological treatment o Suspended film process –

Activated sludge process o Chemical adsorption

Filtration ⇒ Pressure

Sand filters ⇒ Activated

carbon filters ⇒ Micron filters

Sub-surface disposal (ED wells) or Surface disposal to estuary.

Sanitary sewage (offshore)

Segregation Maceration (offshore)

Biological treatment o Fixed film process –

Biotowers, Rotating Biological contactors

Filtration ⇒ Sand filters

Surface disposal of effluent after chlorination into sea. Sludge to be digested.

Sanitary sewage (onshore)

Segregation Equalization

Maceration (offshore)

Biological treatment o Fixed film process –

Biotowers, Rotating Biological contactors

OR o Suspended film process –

Activated sludge process

Filtration ⇒ Sand filters

Surface disposal of effluent after chlorination into rivers. Sludge to be composted.

Cooling water/ storm water (onshore)

Segregation

API/ TPI separation

Filtration – Hay filters

Surface disposal into rivers

13

AB ff ing va osed fT LE-IV : E luent handl riants prop or ONGC

Ankleshw IV heir te hnical constraints an comparatiar Area- and t c d ve

VARIANT IV

lection and mping via

line to ETP F-Gandhar by

ng

Coll d pumping via

cross-country ine to CPF

ar - 45 ine

Disposalpipel

ETP at -

Gandhkms long l

wells by pipeline to ETP at CPF-

Gandhar - 45 kms long line

Disposal into ED

or Water Injecwells by pumping

Collection and

tion pipeETP at CGandhar - kms long line pumping

Disposal into ED

or Water Injection wells by

& Nada

ka North Gandhar

Effluent from Installation (GGS) Dabka

NIL

rth dhar

da

rth r

Nada

Gan&

No No

Na

Dabka Gandha NIL

Nada

Pipelin lea

dditional eff t

Additreatmeatment capa

l effluent Additacity at har

treatmentCPF-GandharCP

nt

Availab ty of ED Availability of ED wells

Availabili

Technicalcons

traints/

requirements

nal E

Gfluen

Additiofor North

D wells andhar t ef

cost Rs.

Approx. Total Effluent 1550 CuM/day 1679 CuM 1679 CuM/day 1679 CuM

quantity

/day /day

28.39 26.84 .27 34.86 46 Capita

costs

I II III

Disposal/ handling mechanism

Colpu

cross-country pipe

at CP- 45 kms long

line

Disposal into ED wells pumpi

ection an

into ED

pumping

Collection and pumping via

cross-country

pumping via

cross-country line to

PF- 45

North Gandhar Dab

Dabka &

Pipeline leakage e leakage Pipeline kage

A luenttre city a

CPF-Gandhar

tionant cap

F-Gand

ional efflue capacity at

iliwells

ty of ED wells

Total Estimated Rs.2409.52 lakhs 2467.71 lakhs Rs.3204.30 lakhs Rs.4253.64 lakhs

l cost outlay Rs. per CuM effluent Considering next 15 years operation considering total effluent production

14

TABLE-V : Effluents generated at ONGC-Hazira Gas Processing Complex and their characteristics

TYPE OF FFLUENT EFFLUENT SOURCE EFFLUENT

CHARACTERISTICSEFFLUENT

TREATMENT PROVISIONS

TREATED EFFLUENT HANDLING E

Prowaste stream (PWS) containing chelow

Gas Sweetening units process funnel

• units p

•

• ery unit process funnel

• units

• Boilers blowdown

Quantities are small Stream flow

OD &

s

chemical

Sulphide is in order of m

present

Collected through the Process Waste

WS)

u

men

umping & treatment for pH, O&G, TSS, COD,

Sulcs correction

Treated effluent is contained in a

. Most

.

gardening. Aquaculture being carrie

rd p

cess •

micals but in sulphur

•

Gas Dehydrationrocess funnel

Condensate Fracunits process funnLPG Recovery uniprocess funnel Kerosene Recov

tionation el t

Sulphur Recovery floor washings

continuous Very high C

BOD valueTEG & MDE Oil & grea

low Emulsifying

present

s (due to A)

e content

s

Stream (Pchannel undergro Final colle

Process WTreat(PWTP) s Further p

0.05 pp Phenolics

running nd ction in aste

t Plant ump

BOD,Phenoli

phide &

guard pondof the effluused as dilwater for SCaustic treatmentRemainingused for

ent is ution pent

. water

d out ond. in Gua

water tem

grease •

hings

or washings

nits floor washings LPG Recovery unit floor

hings

QuantitFlow co

Low COD & BOD

Almost all oil & greasis free, very little emulsion

running undergro

Contaminated RainWater Treatment Plant (CRWTP)Further pumpinremoval of free oil suspended solids

WTP

ffluent water

micals

p ed Treated effluent goes to Final effluent disposal

stem for

Wet air oxidation followed by dilutio

process (biologictreatment) in SC

for gardening

tion

tem rd pond . lution

itary age dings High COD & TSS closed drain disposed of

OilySys(OWS) containing water contami-nated with oil and

• Gas Sweetening units floor was

• Gas Dehydration units flo

• Condensate Fractionation u

• wasKerosene Recovery unit floor washings

• Cooling tower blowdown • Tank farm drainages

ies are large ntinuous High oil & grease

No sulphide present e

Collected through the Oily Water System (OWS) channel

und Final collection in

sump g &

& in

CR

Treated ejoins storm channel. Can be used for gardening, if water is short.

Spent Caustic Stream (SCS) contain-ing high sulphur and alkaline che

• Sulphur Recovery units process funnels

• Caustic Wash units drains

Quantity is small Highly concentrated Very high sulphide

content Alkaline in nature

Collected in Caustic waste its and drainto Spent Caustic Treatment plant (SCTP)

n and high rate activated sludge

al TP

sydisposal or reuse

DiluWater Sys

• Treated Process Waste Treatment plant effluent after Gua

Large quantity Conforming to MINAS

stds

Collected from outlet of PWTP 1& 2 and pumped to SCTP for di

Reuse of treated effluent

SanSewStream

• Sewage water from toilets of all buil

• Canteen waste water

Quantity is regular Collected through

Treated in package Sanitary Sewage treatment plant

Chlorinated and to

storm water drain channel

Storm water system

• Open drains outside process units

• Steam drain traps

Almost pure water Quantity varies

greatly

Collected in underground storm water drains No treatment

Sent out through storm water drain channel

15

Figu of Oi tion facil nt generation pointsre-1 : Schematic sketch l & gas produc ity with efflueP1

P2

P3

P4

s

eTaken from Production Equipment (1996) - Baker Production Servic

gure-2 : Schematic sketch r for Oil & uction Fi cut away of Heater-treate gas prod

16

Well fluid drained From sampling

point

Water drained From Chemical

tanks

Effluent drained From 3-phase

Separators

Effluent drained From Storage

Tanks

Effluent drained From Heater

treater

PRODUCED WATER

STORAGE TANK

Oil pump house/ Compressor

Floor washings OILY WATERSYSTEM (OWS)

OIL/WATER

SEP

Oil recovery

Cooling water Blow down

Rain water/ Storm water

STORM WATER SYSTEM (SWS)

CONTROLPIT/

CHAMBER

Water to open drainSanitary

Sewage

SOAK

PRODUCEDWATER

CONDITION-ING

CONDITIONEDWATER

STORAGE

Treated Effluentfor Re-injection/Reuse/ Disposal

Figure-3 : Graphical representation of effluent handling routes

17 Figure-4 : Diagrammatic representation of Effluent disposal/ reuse mechanisms in vogue

GGS-

-4

GGS-6 WIP-3

GGS-1 CTF-L GCP-1

GGS-9 GCP-2

5

GGS

GGS-3

GGS-2 GGS-8

GGS-7

WIP-1

WIP-2

ETP-1

GGS-ETP-2

Treated Effluent1/ETP-2 Interconnection oil lines

Untreated Effluent lines

ETP-Slop

lines

DML

y)

Flow

rat

e (C

uM/d

aTS

S (m

g/l)

F

Schematic drawing indicating raw effluent, treated effluent and slop oil fLakwa oilfield, Assam

low in Figure-5 :

Flow through ETPs

5000

0

1000

2000

3000

4000

0 50 100 150 200 250 300 350 400

Days

Oil & grease content

100000

/l)

1

10

100

1000

10000

0 50 100 150 200 250 300 350 400

Days

Oil

& g

reas

e (m

g

Total Suspended Solids content

1

10

100

1000

0 50 100 150 200 250 300 350 400

Days

Chemical Oxygen Demand

0

100

200

300

400

500

600

0 50 100 150 200 250 300 350 400

Days

CO

D (

mg

/l)

igure-6 : Graphical presentation of effluent flow and effluent characteristics variation in raw and treated effluents at ETP-I & II, Lakwa using either ETP and combined ETPs in series mode of operation

18

ANKL;

Effluent generation from remote oilfields in Area-IV, Ankleshwar Asset

0

200

400

600

800

1000

1200

1400

1600

1800

2004-05 2005-06 2007-08 2008-09 2009-10 2010-11 2011-12 2012-13 2013-14 2014-15 2015-16 2016-17 2017-18 2018-19 2019-20 2020-21 2021-22 2022-23 2023-24 2024-25

Efflu

ent (

CuM

/day

)

ACTUAL PREDICTION

Figure-7 : Schematic sketch indicating the remote oilfield locations of Area-IV in ONGC, Ankleshwar Asset

JAMBUSAR

BHARUCH

ESHWAR

DEVLA

NADA

RAILWAY LINE TO VADODARA

WN

GGS-NAD

GGS-JAMBUSA

DAB

MALPUR

DEGAM

PADRA TO

HA

MAHI RIVER

DADHAR RIVER

GANDHAR OILFIELD

AREA

GGS-

GAVASAD

GAJERA

GGS-

TO CAMBAY CROSS RIVER MAHI)(A

KARJAN

SARASVANI T-POINT

AMOD TOWN

SARBHAN

GGS-NORTH

VANSETA

NEDRA

KURAL

CSANDH HITRAL17 kms

A

22 kms

14 kms

40

19 kms

MAGNADT-POINT

8 kms INSTALLATION

BUNK HOUSE COLONY

PIPELINE JUNCTION T-POINTS

RAILWAY

OILFIELD AREA OF AREA-IV

Year

DABKA-GAJERA FIELD NORTH SARBHAN FIELD JAMBUSAR FIELD NADA FIELD NORTH GANDHAR FIELD TOTAL : AREA-IV

19

Figure-8 : Actual & prediction effluent generation loads from the remote oilfield locations of Area-IV in ONGC, Ankleshwar Asset

CT kleshw

Main Pump house Old pipeline to river

CETP – BEAIL Ankleshwar BEAIL pipeline to sea Area in which treated effluent is being disposed in

ll

Piludara

Figure-9 : Diagrammatic sketch indicating the effluent disposal routes for effluent from CTF-Ankleshwar

F- An ar

OILY WATER SYSTEM

Gas fromoffshore F

Gas Sweetening

Condensate Fractionation

Gas Dehydration

ARN/ NGL

St

LPG Stoar

LPG Recovery Unit

Utilities – Boilers & Cooling towers

Slug tche

Sulphur

Gas to

SPENT CAUSTIC STREAM

SANITARY

SEWA

Sulphur Recovery

Ca

20

PROCESS WASTE STREAMFigure-10 : Basic process scheme of Hazira Gas Processing Complex indicating the effluent

disposal points and types of effluent generated

1

10

100

1000

0 10 20

BO

D (m

g/l)

Figure-11 : BOD data of processbrought into place

Inlet

30

waste s

Se

InOutlet

40 50 60 70 80

Days

tream before and after seed control mechncism is

ed control mechanism in place

21