Session 1Sludge treatments and their effects onpathogens

Treatment and disinfection of sludge using quicklime

A.D. AndreadakisDepartment of Water Resources, Faculty of Civil Engineering, National TechnicalUniversity of Athens, 5 Iroon Polytechniou St., Zorgafou, Athens 15773, Greece

Introduction

Lime is a readily available alkali, which is widely used in sewage treatment.Utilisation of lime has the following benefits: a) conditions all types of sludge, b)precipitates toxic metals and removes nutrients, c) destroys the pathogenic agents, d)reduces the biochemical and biological oxygen demand and suspended solids, e)eliminates offensive odours.

Two forms of application of lime are usually distinguished: a) as unslaked (quick-)lime - CaO and b) as slaked lime - Ca(OH)2. Furthermore during treatment of sludge,lime can be added to the sludge before thickening, before dewatering, or afterdewatering. No significant difference has been observed between the effect ofhydrated lime and quicklime when treating sludge with high water content, as is thecase of undewatered sludge (Tullander, 1993). In reaction with water CaO within afew minutes forms Ca(OH)2. For that reason if quicklime is used in sludge with a highwater content the same effect will be attained in practice as with hydrated lime, butwith a lower dose of chemicals (1:1.3). As the handling of quicklime is morecomplicated, hydrated lime is normally used in small treatment plants and quicklimein large plants. When quicklime is slaked to the hydrated form, energy is emitted -1160 kJ/kg CaO. Theoretically, 350-400 kg CaO/m3 water can bring the temperaturenear the boiling point. However, as the quantities of lime used in practice normally arerelated to the dry solids content of the sludge, the treatment of undewatered sludgewill not result in any significant rise of temperature.

The effects of liming undewatered sludge, usually at the dose of 10-20 kg/m3 can besummarised as follows: i) improvement of sludge dewatering properties (in somecases in combination with addition of ferrous sulphate or ferric chloride), ii) pHincrease to about 11.5-12, which lasts for about two weeks, iii) no increase oftemperature, iv) inactivation of bacterial and viral pathogens, but limited effect onparasites and v) regrowth of bacterial pathogens.

In the case of dewatered sludge, addition of quicklime, results in a significanttemperature rise and high dry solid content due to evaporation. This in turn leads toimproved sludge handling characteristics and long lasting disinfection.

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This paper deals with quicklime treatment of dewatered sludge and reviews importantaspects of the process involved, such as temperature and dry solids content increase,pH rise and maintenance, sludge sanitation, sludge handling and physicochemicalcharacteristics, nutrients availability to the plant and technological possibilities.

Chemical reactions

Calcium can be easily found in the form of CaCO3. However, addition of CaCO3 tosludge has very limited effect on pathogen destruction, due to the limited pH rise thatcan be obtained up to 8.5. For this reason calcium carbonate is thermally treated at atemperature of 1100-1200 °C, to produce CaO.

CaCO3 + 42.5 kcal →CaO + CO2 (1)

The quality of the final product (quicklime) depends on the quality of CaCO3 and thethermal process and this quality in term determines the rate of temperature increase ofthe subsequent reaction of CaO with water.

CaO + H2O →Ca(OH)2 + 15 kcal (2)

With addition of the appropriate quantity of CaO a pH increase to approximate 12.5can be obtained. However, it should be noted that unless excess CaO is used, aconsequent reduction of the pH can be observed due to the reaction of the producedCa(OH)2 with the CO2 of the atmosphere or that produced due to biological activity.

Ca(OH)2 + CO2 →CaCO3 + H2O (3)

CaCO3 + CO2 →Ca2+ + 2HCO-3 (4)

Temperature and solids content increase

The expected temperature rise can be theoretically estimated assuming that 100% ofthe heat released (1160 kJ/kg CaO) is utilised and considering the specific heat valuesof water, initial solids (TS1) and lime.

∆T=1160x%CaO

4.16(100%–%TS1) + 0.25x%TS1 + 0.3x%CaO(5)

Equation (5) gives an almost linear increase of ∆T with CaO dose. For dewateredsludges with TS content in the range 20-30% respective increases of 3.4 to 3.9 °C foreach percent CaO dose (1% CaO = 10 kg CaO per tonne of sludge) can betheoretically expected. In practice due to heat losses and quicklime quality (less than100% active CaO), the observed temperature increases are limited to 60-82% of thetheoretical values. The time needed to effect the temperature increase isapproximately one to two hours after mixing, depending on lime quality.

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The increase in the solids due to quicklime addition is almost linear. Theoretically thenew solids content (TS2) can be calculated, by considering the chemical reaction (2)as follows:

%TS2=%TS1 + [74/56x%CaO]

x100%100% + %CaO(6)

A further slight increase of solids can occur due to formation of CaCO3 as a result ofreactions with CO2. The solid content increase results in a more compact sludge,which can be stored and handled more easily.

pH increase and maintenance

It has been found (Carl Bro S/A, 1997), that in order to raise the pH in sludge from 7to 12.5, 1.7 mmoles of (OH) are needed per gr TS, so that the buffering capacity ofproteins of sludge is neutralised. Since 56 mg CaO produce 2 mmoles (OH), 50 mgCaO are needed per gr TS. For sludge with 20-30% TS, 1-1.5% CaO are needed toeffect the increase to 12.5. At this dose there is no excess CaO to neutralise CO2 andorganic acids production. Therefore, a higher dose typically above 2% CaO isnormally needed. It is not unusual to use doses in the range 6-10% CaO in order toensure maintenance of the high pH over sufficiently long periods (several months).One of the main reasons for CO2 production and subsequent pH reduction isbiological activity within the sludge. Due to inefficient mixing and lack of bufferingcapacity, at a dose 2% CaO several regions of the sludge are unstable in the sense thatthe pH is lower than 12, thus allowing microbial activity and production of CO2. As aconsequence, a very quick reduction of pH in the whole of the sludge can be observedleading to low pH values to the order of 8-9 within few weeks. The same happens witha dose of 4% CaO, although at a slower rate (a couple of months). For both dosesodours can develop. Sufficiently long periods (over three months) of stable pH around12.5 can be ensured with doses in the range 6-10%.

Another factor that has to be taken into consideration is the reaction with external CO2of the atmosphere and/or CO2 produced by fungi activity at the surface of the sludge.However, with proper storage (low surface area/volume ratios, low temperatures) thisfactor can be minimised.

Sludge sanitation

The effect of CaO on selected bacteriological parameters after mixing is shown inTable 1, which indicates that substantial reduction of pathogens can be achieved evenfor a dose of 2% CaO. However, Tables 2 and 3 show that a reduction of pathogensover prolonged periods (over 1 day) require a dose of over 4% CaO. The effects of theduration time under high pH and of the temperature seem to vary with the pathogentype. Prolonged exposure, over several days, of coliforms to a high pH environmentenhances their removal while increased temperatures appear to be effective only in the

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case of vegetative clostridium perfrigens. Quicklime treatment of sludge is alsoeffective with respect to removal of parasites. Comparative studies of Ascaris ovagrowth with (10% CaO, Table 5) and without CaO (Table 4) addition, reveal thepresence of multicell ova and development of fully grown larva up to 71% in thereference sample, while practically only unicellular ova are observed with quicklimetreatment. Furthermore, Table 6 indicates that the ova can loose the ability to grow,even under favourable conditions after prolonged exposure to a mixture of sludge -CaO (i.e. exposure for five months).

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Table 1: Influence of CaO on bacteriological parameters 4 hours after mixing, 20 °C (Carl BroS/A, 1997).

CaO Dose Coliforms Temperature Streptococcus Clostridium Salmonellaresistant perfrigensColiforms

% number/g number/g number/g number/g number/g0 23x104 49x103 11x104 30x103 Traced in 10 g2 33x101 – <100 18x102 –4 13x101 – <100 14x102 –6 33x101 – <100 13x102 –8 13x101 – <100 9x102 –

10 13x101 – <100 2x102 –

Table 2: Influence of the CaO dose and storage time on the microbial load [Carl Bro S/A, 1997].

Temperature Coliforms Temperature Clostridium perfringens SalmonellaresistantColiforms

Vegetative SporesDays 1 1 14 1 14 1 14 1 14 1 14CaO Dose Identification in

10 g of sludge% °C number/g sludge0 20 10x106 49x104 33x104 49x104 90x103 10x104 90x103 40x103 + –2 20 33x102 46 2.3 <2 30x102 10x102 <10x102 <10x101 – –4 20 70x102 4.9 <2 <2 13x102 6x101 <10 100 – –6 20 70 5.0 <2 <2 12x102 10x101 <10 <10 – –6 26 70 5.0 <2 <2 60x101 <10 <10 <10 – –8 20 63 <2 <2 <2 20x102 100 <10 <10 – –8 28 26 <2 <2 <2 11x102 <10 <10 <10 – –10 20 9 6 <2 <2 18x102 <10 <10 <10 – –10 33 34 5 <2 <2 70x101 <10 <10 <10 – –15 20 33 <2 <2 <2 11x101 <10 <10 <10 – –15 39 11 <2 <2 <2 <10 <10 <10 <10 – –

Table 3: Reduction of the microbial load in terms of negative logarithms (Carl Bro S/A, 1997).

CaO Dose °C after Coliforms Clostridium perfringens1st day

Vegetative Spores% 4 hr 1 day 14 day 4 hr 1 day 14 day 1 day 14 day0 20 – – 1,3 – – 0,1 – 0,42 20 2,8 3,5 5,3 1,2 1,5 2,0 2,0 >4,04 20 3,2 3,2 6,3 1,3 1,8 2,2 >4,0 >4,06 20 3,8 5,2 6,3 1,4 1,9 3,0 >4,0 >4,06 26 – 5,2 6,3 2,2 4,0 >4,0 >4,08 20 5,2 3,2 >6,7 1,5 1,7 3,0 >4,0 >4,08 28 – 5,6 >6,7 1,9 >4,0 >4,0 >4,010 20 3,2 6,0 6,2 1,2 1,7 >4,0 >4,0 >4,010 33 – 5,5 6,3 – 2,1 >4,0 >4,0 >4,015 20 – 5,5 >6,7 – 2,9 >4,0 >4,0 >4,015 39 – 6,0 >6,7 – >4,0 >4,0 >4,0 >4,0

Table 4: Ascaris ova growth (Reference Sample) (Carl Bro S/A, 1997).

GROWTH STAGE DAY0 14 28 42 56 70 150

Non fertilised ova 1 9,6 11,3 9,2 6,7 5,3 3,3Unicellular 99 85 4 0 8 9,7 10Bicellurar 0 1 0 0 1 1Four cells 0 0 0 0 0 0,3 0,3> 8 cell 0 0,7 16,7 24,6 19,2 10,3 13,3Premature larva 0 3,7 11,3 8,5 6,7 3,3 2,8Fully grown larva 0 0 56,7 57,7 59,3 71 69,3TOTAL 100 100 100 100 100 100 100

Table 5: Ascaris ova growth (CaO 10% treated sludge) (Carl Bro S/A, 1997).

GROWTH STAGE DAY0 14 28 42 56 70 150

Non fertilised ova 1 1.3 1.7 0 0 0 0Unicellular 99 98 96 92.3 92.7 99.3 100Bicellurar 0 0.7 1 0 0.3 0 0Four cells 0 0 0.3 0 0 0 0> 8 cell 0 0 1 7.7 3 0 0Premature larva 0 0 0 0 4 0.7 0Fully grown larva 0 0 0 0 0 0 0TOTAL 100 100 100 100 100 100 100

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Other significant aspects

The long term effect of CaO treatment on sludge characteristics is shown in Table 7.Upon quicklime addition, an increase in total solids content and pH is observed, whilevolatile solids content, phosphorus, nitrogen and ammonia contents are reduced. Withstorage over seven months total solids content tends to gradually increase while pH, isslightly reduced, remain however above 12. It is only after a storage period of twoyears that a drastic reduction of pH and alkalinity are observed. The total solidscontent increases significantly, wile the ratio of total solids volatile to total solids isreduced due to degradation of the organic material. This degradation also explains thehigher phosphorus content observed. Sludge obtains a wood-like texture with slightbut not unpleasant odour.

With respect to phosphorous availability to plants, it has been observed (Akrivos et al.,1999), that upon lime addition and pH increase the available phosphorous is limited to

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GROWTH STAGE Ova retention time in sample before cultivation (weeks)2 4 6 8 20

Non fertilised ova 1.7 3.3 0 0 0.4Unicellular 0.7 7.3 11.7 40.7 63.4Bicellurar 0 1.7 2.3 0 2.3Four cells 0 0.3 2.3 0.3 0.6> 8 cell 24 26.7 54.7 37.4 32.7Premature larva 6.3 4.3 7.7 6.3 0.6Fully grown larva 67.3 56.7 21 15.3 0TOTAL 100 100 100 100 100

Table 6: Ascaris ova cultivation in formaldehyde solution 1% after being isolated out ofsample treated with 10% CaO (Carl Bro S/A, 1997).

Table 7: Long term effects of the CaO treatment (10%) on sludge characteristics (Carl BroS/A, 1997).

Parameter Units Days0* 0 14 45 120 210 720

pH 7.1 12.5 12.5 12.5 12.3 12.1 8.4TS g/kg 168 283 292 291 332 303 531TS Volat. g/kg 101 87 86 90 93 104 103TSVol/TS % 60 31 29 31 28 34 19Tot-P g/kg TS 17 9.8 9.6 – 9.3 – 17Tot-N g/kg TS 32 19 17 17 17 17 13NH3-N g/kg 1.5 0.27 0.21 0.27 0.31 0.18 –Alcalinity mmol/kg – – 2390 2700 3080 2700 1340Odours – – – – – –

* Before CaO addition

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approximately 68%. However, with neutralisation to normal pH (as it happens whensludge is introduced to the soil) the available phosphorous is increase to over 90%.

Finally, practical experience has shown that both batch or continuous plug flowsystems can be used for quickliming of sludge and that the most importanttechnological aspect is related to the sludge-CaO mixing efficiency of the system.

Conclusions

Addition of quicklime to dewatered sludge and subsequent storage under a pH of over12 for at least three months ensures a high degree of sludge sanitation. This sludge canbe used as a soil conditioner and fertiliser without any restrictions as far as pathogensare concerned. Even after prolonged storage, there is a very limited reduction ofnitrogen, while the availability of phosphorous for plant growth is high (over 90%)under conditions of neutralised pH, which is very quickly established upon mixing ofthe sludge with the soil. Finally, quicklime treatment improves the handlingcharacteristics of the sludge and allows for long term storage without development ofodour.

Acknowledgements

The results presented in this paper originate from studies conducted by Carl Bro A/Sand the National Technical University of Athens within the framework of a joined EUproject (Hygienic Sludge Management for Agricultural Utilisation), sponsored by theDirectorate-General for Research (formely DG XII) of the European Commission.The contribution of the other partners of the project namely, NAMA ConsultingEngineers and Planners SA, VKI and the Municipal Enterprises of Water andSewerage of Lamia and Rethymnon, is also acknowledged.

References

Tullander V., (1983), “Quicklime treated sludge”, Environmental effects of organic and inorganiccontaminants in sewage sludge, Davis, Hucker & L’Hermite (eds), D. Reidell Publishing Company.

Carl Bro A/S, (1997), “Treatment of Sludge with Lime”, Research Report

Akrivos J., Mamais D., Katsara K., Andreadakis A., (1999), “Agricultural Utilisation of LimeTreated Sewage Sludge”, Proceedings of the Specialised Conference on Disposal and Utilisation ofSewage Sludge, Athens, Greece, October 13-15, 1999.

Anaerobic digestion of sludge: focusing on degradation ofthe contained organic contaminants

Angelidaki, I.1, and Ahring, B.K.1,2

1The Anaerobic Microbiology/Biotechnology groupDepartment of Biotechnology, Building 227The Technical University of Denmark, 2800 Lyngby, Denmark.Tel. +45 45256187; e-mail: ria@ibt.dtu.dk2School of Engineering and Applied ScienceDepartment of Civil and Environmental EngineeringUniversity of California

Abstract

Great interest has been devoted in the recent years for recycling of the waste createdby modern society. A common way of recycling the organic fraction is amendment onfarmland. However, these wastes can contain possible hazardous components in smallamounts, which can prevent their use in farming. The objective in our study has beento develop biological methods by which selected organic xenobiotic compounds canbe biotransformed by anaerobic or aerobic treatment.

Screening tests assessed the capability of various inocula to degrade two phthalates(DBP, and DEHP), four polycyclic aromatic hydrocarbons (PAHs), four linearalkylbenzene sulfonates (LAS) and three nonylphenol ethoxylates (NPEO) underaerobic and anaerobic conditions.

Under aerobic conditions, a large number of the selected xenobiotics could bedegraded by choosing the appropriate inoculum. Aerobic degradation of DEHP wasonly possible with leachate from a landfill as inoculum. Anaerobic degradation ofsome of the compounds was also detected. Leachate showed capability of degradingphthalates, and anaerobic sludge showed potential for degrading PAH, LAS andNPEO.

Furthermore, anaerobic digestion of sludge amended with either pyren and LAS or 4-nonyl phenol and DEHP in continuously stirred tank reactors showed anaerobictransformation of the tested compounds.

The results are very promising as they indicate that a great potential for biologicaldegradation is present, though the inoculum containing the microorganisms capable oftransforming the recalcitrant xenobiotics has to be carefully chosen.

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Introduction

Within the European Union the total amount of produced sludge is about 6.5 milliontons per year (Smith 1996). There are several disposal routes for sludge, includingocean dumping, incineration, spreading on agricultural land, soil incineration, landspreading in forestry or landfilling. At present the disposal of sludge on landfills iswith 40% the most important outlet in the EU while 37% of the sewage sludgeproduced within the EU was used for agricultural purposes in 1994 (Hall 1994). Theamount of sewage sludge requiring disposal is expected to increase significantly in thefuture due to recent environmental developments. The Helsinki agreement called forthe banning of ocean sludge dumping by 1987 and the Urban Waste Water Directive91/271/EEC, required waste water treatment plants with secondary treatment andnutrient removal in sensitive areas (Kiely 1997). With increasing sludge protection inthe EU larger larger amounts of sewage sludge will be recycled for agriculturalpurposes (Smith 1996). This approach seems to be reasonable since agricultural landcan become nutrient deficient due to intensive cultivation.

In addition to sewage sludge other wastes such as organic industrial wastes, manures,and organic household waste can with great advantage be recycled and used infarmland as fertilizers and as soil improving components.

However, this type of waste can contain possible hazardous components in smallamounts, which might show adverse effects on the ecosystem, e.g. the farmlandamended with sewage sludge. Indeed, linear alkylbenzene sulfonate (LAS) compoundssuch as those used in household detergents, nonylphenols, nonylphenol ethoxylates,polycyclic aromatic hydrocarbons (PAH), and phthalates have recently been identifiedas major anthropogenic organic components in sewage sludge. There is a special publicconcern about organic components, which may have a potential for acute toxicity,mutagenesis, carcinogenesis or teratogenesis or posses estrogenic effects.

The concentrations of LAS in raw wastewater have been reported to range from 3mg/l to 21 mg/l (Brunner et al., 1988, De Henau et al., 1989, Holt et al. 1995, RuizBevia et al., 1989). Although LAS and other common surfactants have been reportedto be readily biodegradable by aerobic processes, much of the surfactant load into asewage treatment facility (reportedly 20-50%) is associated with suspended solids(Greiner and Six 1997, and McAvoy et al. 1998) and thus escapes aerobic treatmentprocesses. LAS is reported not to be biodegraded by anaerobic biological processesusually employed in sludge stabilization (McEvoy and Giger, 1985; Swisher, 1987),and it may be found in the gram per kilogram range in anaerobic sludge. According toMackay et al. (1996) the emission of LAS to soil is predominant due to sludgeapplication on agricultural soil and landfilling. The presence of surfactants in sludgemay have undesirable environmental effects since the surfactant molecules may leachto groundwater contributing to groundwater contamination.

Alkylphenol ethoxylates such as NPnEOs is a group of non-ionic surfactants withworld-wide application and are evidently less biodegradable than LAS (e.g. Swisher,1970; Steinle, 1964; Pitter, 1968) and a wider range of removals from 0-90% based onspecific analyses such as UV and IR spectroscopy (Swisher, 1970). This suggests that

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only partial degradation occurs, such as conversion from polyethoxylates tononylphenol diethoxylate (NP2EO), nonylphenol monoethoxylate (NP1EO), andnonylphenol (NP). The latter is the most recalcitrant of the intermediates formedduring alteration of the NPnEO molecules. Mass balances done on treatment plants inSwitzerland (Brunner et al., 1988) support these findings.

Due to the low water solubility and lipophilic properties of PAHs, these compoundsare removed from sewage partly by biodegradation, partly by adsorption on to sludge.According to Bodzek et al. (1997) PAHs are found in significant amounts in sludge(up to 2000 mg/kg sludge dry mass). The PAHs are mostly originating from fossil fuelcombustion and industrial processes (Shuttleworth and Cerniglia 1995). Generally thehalf-lives of PAHs is increasing with increasing number of aromatic rings, though thedegradation rates is dependent upon the test system. Due to the great adsorptionabilities of PAHs they will precipitate with the particular material in the pre-clearingtank. The sludge originating from this step has a high content of easily degradableorganic material, which is used for the production of methane. PAH are, however, notas easily anaerobically degradable as under aerobic conditions and they tend toaccumulate in the digested sludge.

Sewage sludge and compost contains relatively high concentrations of di(2-ethylhexyl)phthalate (DEPH) and di-n-butylphthalate (DBP) (Danish EnvironmentalAgency, 1996). It was reported that these compounds probably originate from bothhouseholds and industries. DEHP accounts for 90% of the phthalate production world-wide. At least 95% of the DEHP produced is used as an additive in PVC plastics whichare made into various products such as waterproof clothing, footwear, toys, bloodbagsand heat-seal coatings on metal foils. Plastizisers are poorly soluble substances andwill be removed in the waste water treatment plant by biodegradation, though alsoadsorption on sewage sludge is significant. Hence, plastizisers will be transferred tosoil with application of sludge on agricultural land or landfilling of sludge.

Biological treatment of wastes containing toxic compounds could be an effective andcheap method for detoxifying the wastes. In order to do so, microorganisms that candegrade the compounds are needed. In the present study we report results from ascreening of microorganisms capable of degrading LAS, nonylphenols,nonylphenolethoxylates, PAH and phthalates.

Materials and methods Description of the experimental set-up

The tests were performed in batch serum vials where pressure and/or substanceconcentration was followed over time. Two different media were used, one for theanaerobic (Angelidaki et al. 1990) and one for the aerobic inocula, containing per literof water (Milli-Q) 0.8 g K2HPO4, 0.2 g KH2PO4, 0.05 g CaSO4*2H2O, 0.5 gMgSO4*7H2O, 0.01 g FeSO4,*7H2O, 1.0 G (NH4)SO4.

Three sets of control vials (sterile, substrate-unamended, and uninoculated) weremade in triplicates.

Compounds tested

Of PAHs naphthalene, 1-methylnapthalene, fluoranthene, phenanthrene and pyrenewere chosen. The PAHs were added either as a mixture of the five PAHs mixed inequal amounts or as the individual compounds. Among the phthalates, DBP, andDEHP were selected. LAS was used as a mixture of LAS with an alkyl chain length of9 to 13 units and among the nonylphenols 4-Nonylphenol and Nonylphenol mono anddiethoxylate were used. For the mixture of PAH the concentration was counted as thesum of the five compounds.

Inocula

The inocula originated from several different Danish environments as shown in Table1, along with redox conditions, and xenobiotics used during the screening test.

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Table 1: Inoculum identification (original environment), redox conditions forbiotransformation studies, and xenobiotics used.

Origin Redox conditions Xenobiotics addedActivated Sludge Lundtofte Anaerobic, aerobic NPE, LAS, Napthalene,

1-Methylnapthalene, Fluoranthene,Phenanthrene, Pyrene, DBP, DEHP

Activated Sludge Damhuså Anaerobic, aerobic NPE, LAS, Napthalene, 1-Methylnapthalene, Fluoranthene,Phenanthrene, Pyrene, DBP, DEHP

Dewatered sludge Damhuså Anaerobic NPE, LASBiosludge Lundtofte Anaerobic, aerobic NPE, LASSediment Damhuså stream Anaerobic NPE, LAS Sediment Lake Arresø Anaerobic, aerobic NPE, LAS, DBP, DEHPSoil Nr. Herlev, Hillerød Anaerobic, aerobic NPE, LAS, Napthalene,

1-Methylnapthalene, Fluoranthene,Phenanthrene, Pyrene, DBP, DEHP

Soil Møllehøj, Arresø Anaerobic, aerobic NPE, LAS, DBP, DEHPSoil Colgate-Palmolive Anaerobic, aerobic NPE, LASSoil Oil contaminated, Jutland Napthalene, 1-Methylnapthalene,

Fluoranthene, Phenanthrene, PyreneSoil Hjørring Gaswork Napthalene, 1-Methylnapthalene,

Fluoranthene, Phenanthrene, PyreneCompost AFAV, Hillerød Anaerobic, aerobic NPE, LAS, DBP, DEHPGranular sludge UASB reactor, Anaerobic, aerobic NPE, LASEerbeekManure Mesophilic CSTR Anaerobic, aerobic NPE, LASLandfill leachate DBP, DEHP

Reactor experiments

Two reactors of total volume of 4.5l were operated with anaerobic digested sludge at aretention time of 15 days at 37 °C. After the reactors had been operated for a monthwith the sludge additional 4-NP or pyren was added to the feed at day 7 to the reactorR1 and R2 respectively. At day 28 the concentrations of the added compounds wereincreased from 50 ppm to 100 ppm. At day 38 was DEHP and LAS was additionallyadded to the reactors R1 and R2 respectively.

Analysis

Concentration of PAHs, phthalates, was made by GC-MS. While LAS and nonylphenols were measured by HPLC analysis.

Results and discussion

Vials incubated under aerobic conditions showed a decrease of the initial pressurewhen degradation was present. In figure 1 the degradation of PAH is shown wheninoculating with sludge amended soil. When PAH was added in a concentration of 20,100 or 200 ppm the pressure in the vials decreased, indicating degradation of theadded compounds (Fig. 1a). In the PAHs unamended controls the pressure slightlydecreased relative to the sterile control due to digestion of ethanol, though thepressure remained higher then the PAH amended vials. In figure 1b the concentrations(in area counts) of the individual PAH are shown at the start and end of theexperiment. There was a significant reduction of the concentrations of the measuredPAH at the end of the experiments compared to the initial concentrations, confirmingthat the PAHs were biodegraded.

In figure 2 degradation of DBP under anaerobic conditions is shown. When degradationoccured the pressure in the vials increased due to production of methane and carbondioxide. The pressure of the controls without DBP addition also increased due tomineralization of organics contained in the inoculum and ethanol added in aconcentration corresponding to the DBP amended vials. However, the pressure increasein the vials with 20 and 100 ppm DBP was higher than in the controls, corresponding tobiodegradation of DBP. Vials with 200 ppm DBP showed no increase of the pressureindicating that this concentration was toxic to bacteria preventing both degradation ofDBP and of the organics contained in the inoculum. In figure 2b the concentration ofDBP (20 ppm and 100 ppm) is reported and evidence of DBP biodegradation is givenwhen evaluation the pressure increase together with the DBP concentration decrease.

The results from the screening test are summarized in Table 2. Most compounds weredegraded both under aerobic and anaerobic conditions. Some compounds were easilydegradable with most inocula. Such compounds were naphthalene, DBP, while the restcompounds showed only degradation with only a few inocula. DEHP is a compoundthat has been reported as recalcitrant under anaerobic conditions. Ejlertson (1997) hasreported that DEHP was unaffected, during anaerobic incubation, throughout an

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Time (weeks)0 2 4 6 8 10

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phenanthrene fluoranthrene pyrene0

1e+6

2e+6

3e+6

4e+6

5e+6

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begining

end

Figure 1: Pressure depletion in PAHs amended aerobic vials and relative concentration in vialsat the beginning and end of the experiment.

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Time (weeks)

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Figure 2: Pressure increment in DBP amended anaerobic vials and relative concentration invials at the beginning and end of the experiment.

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experimental period of 330 days. However, in our screening experiments we foundindication of degradation of DEHP with inoculum originating from leachate from alandfill. It is possible that deposition of plastics, and other materials containing DEHPhas favoured the selection of organisms capable of degradation of DEHP. The landfillpercolate did not show capability of aerobic degradation of DEHP.

LAS is known to be easily degraded aerobically, e.g. in activated sludge reactorsduring waste water treatment, but is not degraded anaerobically in the waste watertreatment (McEvoy and Giger 1985). In our screening experiments we found inoculashowing anaerobic capability of LAS. Inoculum from lake sediment (Damhuså)showed capability of anaerobic degradation of LAS. In addition, also inocula thatwere found in aerobic environments such as compost and activated sludge (Lundtoftewastewater treatment plant) showed capability of anaerobic degradation of LAS.

PAHs were found to be degradable under both aerobic and anaerobic conditions,though a higher number of inocula contained the relevant microorganisms for aerobicPAH degradation.

From the reactor experiments it can be seen that all the tested compounds weretransformed under anaerobic digestion of sludge. Reduction of the compounds to upto 100% were observed (Figure 3 and Fig. 4). After additions of the second xenobioticcompound in the reactors at day 38 initial disturbance of the process with temporarydecrease of the transformation of the PAH and DEHP was observed. However, afterapproximately 10 days a good transformation of the compounds was reestablished.

Conclusions

The screening test showed that a range of inocula have a high capacity towardsdegradation of recalcitrant xenobiotic compounds. Especially the degradation ofDEHP and LAS under anaerobic conditions is promising considering the importance

Table 2: Results from the screenings test for degradation of xenobiotic compounds.

Group Tested xenobiotic compound Aerobic AnaerobicLAS Linear Alkylbenzene Sulfonate + +NPE 4-Nonylphenol – –

Nonylphenolmonoethoxylate + +Nonylphenoldietoxylate + +

PAH Acenapthene – +Naphthalene + +Phenanthrene + +Fluoranthene + –Pyrene + +

Phthalate DEHP + +DBP + +

+: indicates degradation; -: indicates not degradation;

of eliminating these compounds during waste water treatment. The discovery of newbacteria gives the possibility of bioprocessing waste containing toxic compounds byintroducing the appropriate bacteria into, for instance, a biogas reactor system, wherethe organic matter of the waste will be converted into biogas with simultaneousdegradation of organic contaminants. The effluent from such a process could then beapplied on agricultural soil as a fertilizer and soil improver component.

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Figure 3: Anaerobic CSTR reactor experiment (Reactor 1). Feed with anaerobic sludge containingsmall concentrations of xenobiotics. At day 6 was the feed amended with 50 ppm 4-pyren whichwas increased to 100 ppm at day 28. At day 39 was additionally added 50 ppm LAS12.

Figure 4: Anaerobic CSTR reactor experiment (Reactor 2). Feed with anaerobic sludgecontaining small concentrations of xenobiotics. At day 6 was the feed amended with 50 ppm 4-NPwhich was increased to 100 ppm at day 28. At day 39 was additionally added 100 ppm DEHP.

Acknowledgements

This work was supported by grants from The Strategic Environmental Researchprogramme 1997-2000 (Subprogramme on sustainable land use).

References

Angelidaki, I., Petersen, S.P. and Ahring, B.K. (1990) Effects of lipids on thermophilic anaerobicdigestion and reduction of lipid inhibition upon addition of bentonite. Appl. Microbiol. Biotecnol. 33,469-472.

Bodzek, D., Janoszka, B., and Dobosz, C., (1997) Determination of polycyclic aromatic compoundsand heavy metals in sludge from biological sewage treatment plants. Journal of Chromatography A774, 177-192.

Brunner, P.H., Capri, S., Marcomini, A. and Giger, W. (1988) Occurrence and behaviour of linearalkylbenzenesulphonates, nonylphenol, nonylphenol mono- and nonylphenol diethoxylates in sewageand sewage sludge treatment. Water Res. 22, 1465-1472.

Danish Environmental Protection Agency. (1998) Indsamling og anvendelse af organiskdagrenovation i biogasanlæg. Miljøprojekt 386 (in Danish).

Henau, H. De, Matthijs, E. and Namkung, E. (1989) Trace analysis of linear alkylbenzene sulfonate(LAS) by HPLC. Detailed results from two sewage treatment plants. In Organic Contaminants inWaste Water, Sludge and Sediment. D. Quaghebeur, I. Temmerman and G. Angeletti editors.Elsevier Applied Science, London.

Holt, M.S., Waters, J. and Comber, M.H.I., (1995) AIS/CESIO environmental surfactant monitoringprogramme. SDIA sewage treatment pilot study on linear alkylbenzene sulphonate (LAS). Water Res.29, 2063-2070.

Kiely, G., (1997) Environmental engineering. McGraw-Hill (ed.). pp. 574-583, 605-611.

Mackay, D., di Guardo, A. and Paterson, S. (1996) Assessment of chemical fate in the environmentusing evaluative regional and local-scale models: illustrative application to Chlorobenzene andLinear Alkylbenzene sulfonates. Environm. Toxicol. and Chem. 15,1638-1648.

Mahajan, M.C., Phale, P.S. and Vaidyanathan, C.S. (1994) Evidence for involvement of multiplepathways in the biodegradaton of 1- and 2-methylnaphthalene by Pseudomonas putida CSV86. Arch.Microbiol. 161, 425-433.

McAvoy, D.C., Dyer, S.D. and Fendinger, N.J. (1998) Removal of alcohol ethoxylates ,alkylethoxylate sulfates, and linear alkylbenzene sulphonates in wastewater treatment. Environm. Toxicol.and Chem. 17, 1705-1711.

McEvoy, J. and Giger, W. (1986). Determination of linear alkylbenzenesulfonates in sewage sludgeby high-resolution gas chromatography/mass spectrometry. Environm. Sci. Technol. 20, 376-383.

Quaghebeur, D., Temmerman, I. and Angeletti, G. (editors). Elsevier Applied Science, London.

Pitter, P. (1968) Relation between degradability and chemical structure of nonionic polyethyleneoxide compounds. Surf. Cong., 1, 115-123.

Ruiz Bevia, F., Prats, D. and Rico C. (1989) Elimination of L.A.S. (linear alkylbenzene sulfonate)during sewage treatment, drying and compostage of sludge and soil amending processes. In OrganicContaminants in Waste Water, Sludge and Sediment. D. Quaghebeur, I. Temmerman and G.Angeletti editors. Elsevier Applied Science, London.

Shuttleworth, K.L. and Cerniglia, C.E. (1995) Environmental aspects of PAH biodegradation. Appl.Bioch. and Biotechnol. 54, 291-302.

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Smith, S.R., (1996) Agricultural recycling of sewage sludge and the environment. Wallingford.

Steinle, E.C., Myerly, R.C. and Vath, C.A. (1964). Surfactants containing ethylene oxide:Relationship of structure to biodegradability. Jour. Amer. Oil Chemists Soc. 41, 804-807.

Stringfellow, W.T. and Aitkin, M.D. (1995). Competitive metabolism of naphthalene,methylnaphthalene and flourene by phenanthrene-degrading pseudomonads. Appl. Environ.Microbiol. 61 357-362.

Swisher, R.D. (1987). Surfactant Biodegradation. Marcel Dekker, New York.

Volkering, F., Breure, A.M. and Andel, J.G. 1993. Effect of micro-organisms on the bioavailabilityand biodegradation of crystaline naphthalene. Appl. Microbiol. Biotechnol. 40, 535-540.

49

Thermal drying – microbiological quality of dried sludge

Jean Paul ChabrierENVIRO-CONSULT32 rue de l’Est, F-68110 IllzachTel : 00 33 3 89 53 54 71 - Fax : 00 33 3 89 53 19 20

IntroductionThe main use of urban sewage sludge for most European countries is the recycling toagriculture.

Different pathogens such as viruses, bacteria, protozoa and parasites can be found inthe sludge produced by the waste water treatments plants (Faust, 1976; Schwartzbrodet al., 1986; Yanko, 1988).

The sanitary risk due to pathogens must be taken into account; however studies on thecapacity of living of these pathogens and parasites (Engelberg, 1985) like Helmintheggs confirmed the resistance of the eggs to most biological treatments such asaerobic stabilisation, mesophilic anaerobic digestion and lagooning. After applyingother biological and chemical treatments (composting, liming) the viability of theparasite eggs clearly shows the necessity of precisely defining the process parameters(temperature, pH, homogenisation, treatment time, end process heat value…) in orderto efficiently destroy the Helminth eggs.

It is generally demonstrated that heat is a powerful virus killer. The thermophilicaerobic digestion and pasteurisation remain attractive processes to inactivate virusesand other pathogens (60 °C for a treatment contact time superior or equal to an hour).The bacteria indicating faecal contamination are destroyed for processing temperaturetreatments superior or equal to 80 °C – that is always the case for drying. However theneed to reach such a temperature involves important energetic costs (in thermal dryingapproximatively 900 to 1,200 kWh per tonne of evaporated water – ENVIRO-CONSULT measurements) if the route is only sludge recycling to agriculture.

Does the sludge microbial quality on its own justify the application of thermaldrying technologies? The author, through his experience, will bring elements toanswer this question.

Reminder of applicable legislation1

The applicable legal texts are very different from one country to another. They can besummarised as follows:

1Report Recommendations to preserve and extend sludge disposal routes, CEN/TC 308/WG3 N33.

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Table 1: Regulations on sanitary sludge quality.

2 Third Report of the ATV/VKS Working Group 3.2.2 on Disinfection of sewage sludge.

Country Recommended treatments: End product standardslegal guidelines and laws

European Union Sludge treatment by biological, –chemical, thermal treatment, storage or any other specific process

Germany Sewage Sludge Ordinance (AbfKlärV2) Only sewage sludge consideredas safe from an epidemic-hygienicpoint of view and land for foddercultivation

France Definition in the 97-1133 decree: Only for hygienised sludge:Treatment by physical, biological, Salmonella: < 8 mpn/10 g dmchemical or thermal process, for long Enteroviruses: < 3 cfumpn /10 g dmchemical or thermal process, for long viable Helminths eggs:term storage, or by any other < 3 per 10 g dmappropriate process, in order to Thermo-tolerant coliforms: nonesignificantly reduce its fermentationcapacity and the correlated sanitaryrisks by using it

Denmark - Thermal treatment at 70 °C –during an hour or equivalent combinations of time and temperature

- Composting at 55 °C during at least 15 days

- Liming- Aerobic and anaerobic treatments

Austria Salmonellae: none in 1 g dmIn the three Enterobacteriacaee: < 1000 in 1 g dmfollowing three Helminth eggs: none in 1g dmLänder: - Burgenland- Ober Österreich- SalzburgSwitzerland – For the agricultural land

producing fodder or vegetables: Enterobacteriacaee: < 100 in 1 g dmInfectious parasite eggs: none in 1 g dm

Italy – Salmonellae: < 1000 in 1 g dmLuxembourg – Enterobacteriacaee: < 100 in 1 g dm

Viable parasite eggs: none in 1 g dmUSA Application of EPA 92 40 CFR or Salmonellae: < 3 mpn or PFU in 4 g dm

PART 503 Enteroviruses: < 1 PFU in 4 g dmProcess to further reduce pathogens: Viable Helminth eggs: < 1 in 4 g dmPFRP – class AProcess to significantly reduce Feacal coliforms: < 2 106 in 1 g dmpathogens: PSRP – class B

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The control of the sludge microbiological contamination can be considered in threeways:

• Either by applying specific and homologated treatment processes to the sludgewhich leads to the non detection (in case of thermal treatment by drying) or thereduction of pathogenic germs concentration;

• Or by making tests controlling the microbiological quality of the sludge;

• Or else by simultaneously applying both preceding operations.

Analysing the existing situation, we can divide the European countries into fourgroups:

The French rules are placed between group 1 and group 3 because onlymicrobiological limits are set up for sanitary quality (hygienised sludge). However,for the determination of pathogens limits, it applies the American analysis methods.

Therefore, in front of these established facts, what is the best approach to consider?

In France, what is the present situation for stabilisation andmicrobiological treatments?

The situation is as follows:

The use of mesophilic anaerobic digestion was little developed in the 1980s. Most ofthe treatment plants applying this process were built in the 1970s and for thirty years afew new plants have been equipped. From this specific situation, two major problemsappeared: the lack of sludge stabilisation (smells , harmful effects during storage) andof microbiological quality even though that one is only partial for the already settledprocesses.

To improve the situation, the sludge post-treatment with lime was largely applied inmedium-size plants of 20-150 000 p.e. or even bigger.

In 1997, Article 7 of the 97-1133 decree introduced by a compulsory point of view aphysical, biological, chemical or thermal treatment of the sludge as well as a long

Table 2: Classification according to the microbiological quality.

Group Definition of the rules CountryN° 1 Slight recommended rules: European Union

Little compulsion on the stabilisation and microbiological processes GermanyN° 2 Authorised processes in terms of reduction or removal of pathogens DenmarkN° 3 Conformity to a specified microbiological quality and for specific uses Switzerland,

AustriaN° 4 Answers related to limited values and authorised processes through USA

EPA 40 CFR – PART 503

storage in order to significantly reduce its fermentation and sanitary risks when used.The decree application continued to boost the liming process. Lime is generally wellaccepted by farmers who actively participate in sludge recycling.

When comparing the French situation of sludge spreading to the US EPA rules on≤vector reduction” – i.e. management practices that reduce the attraction of insects,animals, etc – the following table can be made:

Up to now in France drying is not much developed in comparison with most of otherEuropean countries (number of 'drying lines' in Europe: approx. 400 – in France: 30 ofwhich 20 in operations and 10 in construction – ENVIRO-CONSULT Data).

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Table 3: Process limiting the vector attraction.

Often applied treatments Treatments sometimes Treatments rarely or not yet applied applied

Ploughing in the soil within - anaerobic digestion - aerobic thermophilic digestion24 to 48 hours after spreading - lime conditioning - soil injection(97-1133 Decree) - increase of dm content to more

than 75 or 90%

Graph 1: Thermal drying in Europe (source: Enviro-Consult).

Note: the thermal drying is in great development in the United Kingdom.

Present techniques used in France

A last point on the French situation concerns the present methods used in thelaboratories to determine the parasites. According to the opinion of many Frenchexperts, the analysis methods of EPA cannot guarantee that the results obtained willbe validated.

Eight techniques are available to enumerate and test the Helminth eggs viability andthe technique which would lead to the most important number of eggs would be theone identified by AES3.

In France a big question is being discussed nowadays by experts, which is : “Dowe have to move towards an experimental norm and therefore question theregulatory texts?”

Parameters and treatments to be used in the control of themicrobiological contamination

The reduction or removal of pathogens is influenced by different factors and by theapplied treatments: • Setting velocity: for Helminth eggs it varies from 0.65 m/s for Ascaris eggs to 12.5

m/s for Schistosoma (Shuval, 1986).• Heat and exposition time: graphs 2, 3 and 4 (taken from Sanitation and diseases:

Health aspects of excreta and waste water management) show the influence oftemperature and exposition time for the destruction of- Ascaris eggs (Feachem et al., 1983)- Salmonellae (Feachem et al., 1983)- Enteroviruses (Feachem et al., 1983)

• physical treatments: irradiation, ultrasounds, long term storage• biological treatments: thermophilic aerobic and anaerobic digestion, composting• chemical treatments: fertilisers effects and lime conditioning

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3 AES = Antiformine, ethylacetate, zinc sulphate: method developed by Gaspard and Schwartzbrod(1995).

Thermal drying: heat and exposure time

The thermal drying is a physical operation which consists in draining all or part of thewater contained in the dewatered sludge.

Drying is made at the atmospheric pressure and the evaporated vapours are condensedinto a condenser installed on the line (vapour circuit).

There are three main types of thermal drying technologies:• Indirect drying or by contact: the heat is transferred to the wet sludge which is

deposited on a hot plate, thus allowing the evaporation of the water.• Direct drying or by convection: the heat is transferred directly from the energy

carrier (flue gas) to the wet prepared sludge, thus the flue gas absorbs the humidityof the sludge.

• Mixed drying: it is a combination of drying by contact and by convection.The used heating medium depends on the applied technologies:For the indirect drying: saturated steam, thermal-oil.For the direct drying: exhaust flue gas, warm air or gas.

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Graphs 2: Effect of the relationtemperature/time on the destruction ofAscaris eggs.

Graphs 3: Effect of the relationtemperature/time on the destruction ofEnteroviruses.

Graph 4: Effect of the relationtemperature/time on the destruction ofSalmonella.

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Graph 5: ENVIRO-CONSULT Data.

The reached temperatures vary according to the processes and the sludge drying phase.

Black (thin) curve: thermogravimetric curveGrey (thick) curve: sludge temperature increasement curve

Microbiological quality results

The following values were found on samples of pre-dried sludge (55% dryness) andfull dried sludge up to 90 % dryness.

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Table 4: Temperature of sludge and gas (source: ENVIRO-CONSULT).

Drying technology Temperature of Heat of vapours or End sludge drynessdried sludge flue gas %

Drum dryer 84 °C 140 °C 95Fluidized bed dryer 87 °C > 110 °C 95Thin film dryer* 95 – 100 °C 100 °C 65Discs dryer** 112 – 118 °C 120 °C 95

*very high transmission coefficient λ = 100 W/mK.** residence time in dryer: 1h30mn maximum

Table 5: Results on the sludge microbiological quality – data collected by ENVIRO-CONSULT.

Pathogens Legal requirements Experimental dataFrench EPA 503 Digested Digested Digested Digested DigestedDecree of dried sludge dried sludge dried sludge predried dried sludge8.01.98 UWWTP UWWTP UWWTP sludge UWWTP

Baltimore Nancy Brugges* UWWTP Zurich***Zurich**

Salmonellae < 8 mpn/10 g < 4 mpn/4 g Absence /25 g Absence / 10 g Absence / 25 g < 1 < 1MS MS

Enterovi- < 3 mpn PFU/ < 1 PFU/4 g Undetermined Absence Undetermined Undetermined Undeterminedruses 10 g MS MS beforeEntero- thermalbacteriaceae treatmentViable < 3/10 g MS < 1/4 g MS Absence/25 g Absence/10 g Undetermined < 1 < 1 Helmintheggs Thermo- – < 1000 < 10 Undetermined < 10 < 1 < 1tolerant mpn/g MScoliforms

* Digested dried sludge have been stored in bags during one year. One analysis sample was takenfrom the storage (Seghers Better Technology Company).

** Indirect drying during 5 minutes residence time at 95-100 °C from sludge side and 160 °C fromheat side. This drying conditions fullfills the EPA rules for class A, however the end dryness isvery low (55%) and a recontamination is always possible except for parasites like Ascaris eggs(Buss AG, Basel).

*** Indirect drying with a residence time of 45 minutes (Buss AG, Basel).

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CONCLUSIONS

Important studies on the sanitary quality of the dried sludge have not been made up tonow in France and neither were we able to find data for Germany.

Results obtained were supplied by various dryers and process manufacturers duringspecific tests but very few information were given on the methods of making thesampling or the analysis methods used.

No presence of viable Helminth eggs is established after drying; according tobiologists, their survival is impossible and therefore it can be assumed that the driedsludge cannot be contaminated again because of the storage conditions, even thoughthis one can be long.

If the thermal drying is interesting in the stabilisation or microbiological quality,nonetheless its first advantage is the reduced volume and mass of the sludge in orderto find out new energy and materials routes for recycling in which the microbiologicalquality is of little interest.

REFERENCES

CEN/TC 308/WG 3 Report 1999 – 09: Recommendations to preserve and extendsludge utilisation and disposal

3rd Report of the ATV/VKS Working Group 3.2.2 «disinfection of Sewage Sludge».

ENVIRO CONSULT data board – European sludge drying market analysis – 1998.

Gaspard (1995) THESIS : Environmental parasites contamination : prospective for asanitary risks management - .NANCY France.

Richard G. Feachem, David J. Bradley, Hemda Garelick and D. Ducan MaraSanitation and disease - Health aspects of excreta and wastewater management.

Schwartzbrod J, Gaspard P, Thiriat L -Volume 1, number 2, 1998 European WaterManagement, Pathogenic micro-organisms in sludge and effect of various treatmentprocesses for their removal.

A survey of E.coli in UK sludges: UK water industry research limited – examplesgiven by Tim EVANS.