e> Pergamon War. Sc,. T~ch. Vol. 33, No. 8, pp. 89-94, 1996. Copynghl © 1996 IA WQ. Published by ElsevIer Science LId

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AEROBIC THERMOPHILIC COMPO STING OF PIGGERY SOLID WASTES

S, M. Rao Bhamidimarri and S. P. Pandey

Department of Process and Environmental Technology, Faculty of Technology, Massey University, Private Bag 11222, Palmerston North, New Zealand

ABSTRACf

Aerobic static pile composting of piggery solids was investigated at a 5 m3 scale. Sawdust was used as the bulking agent to provide additional carbon and to increase the porosity of the substrate. The temperature profiles indicated that the solid waste could be pasteurised completely. The nutrient analysis showed that 79% of initial nitrogen was conserved in the compost while there was no significant change in phosphorus concentration. The mIcrobiological assays revealed that there was a four orders of magnitude decline in Enterococci counts while the MPN counts decreased by three orders of magnitude suggesting there may be spore-forming bacleria surviving the composting process. Copyright © 1996 IAWQ. Published by Elsevier Science Ltd.

KEYWORDS

Thennophilic composting; piggery solids; static pile; bulking agent; nutrients; bacterial counts.

INTRODUCfION

The pig industry has seen a steady growth in recent years in New Zealand. Piggeries have been identified among the agricultural and livestock industries as the most significant point source contributors to surface and ground water pollution. The characteristics of raw piggery solid waste vary according to age, physiological stage, nature of feed and the production practices. Vanderholm (1984) illustrated the likely characteristics of raw pig manure in New Zealand piggeries. Hydraulic flushing is popularly used (Warburton, 1980) to remove the waste from the housing. Typical pig manure characteristics are given in Table I.

The nutrient rich solid waste from piggeries is an ideal substrate for composting and nutrient recycling.

Composting is an aerobic thermophilic decomposition of organic matter. It is a low cost organic solid waste stabilization process in which the decomposition of organic matter is carried out mainly by aerobic bacteria, fungi, actinonycetes and protozoa. The biology of composting is widely described in literature (Finstein and Miler, 1985; Stentiford, 1987). In New Zealand, composting of meat industry solid wastes has been practised for several years (Keeley and Skipper, 1988).

89

90 S. M. RAO BHAMIDIMARRI and S. P. PANDEY

Table I. Freshly voided pig manure characteristics in meal fed piggeries (Vanderholm. 1984).

Animal weight 50 kg

Raw manure 3.30 kg/day (urine and faeces)

T ctal solids (TS) 0.30 kg/day

VoIatnl solids (VS) 80~ TS

BOD 0.10 kg/day

COD 2.9 x BOOs

Total N 0.023 kcvday

Total P 0.008 kg/day

Total K 0.015 kg/day

During the composting process. the organic content is converted to more stable and products as below.

Biodegradable + organic waste

microrganisms ----»

Stabilized organic residue + microbial biomass + CO2 + H20 + Heat

The temperature development during composting is critical to the process. Temperatures of around 700C are desirable for both organic stabilization and for pathogen and parasite inactivation. However. high temperatures over 750C could lead to conditions which inhibit the microbial activity (Gotaas. 1956). If ventilation is impeded due to either high moisture content or inadequate bulking material. anaerobiosis occurs and significant odour problems develop (Bogoni. 1988). The composting technologies that are currently available fall into two categories. either open systems such as winrows (conventional and aerated) and aerated static piles (Wilson. 1983) or closed reactor systems in which the composting material is continuously mixed (Haug, 1980). The open systems are relatively more difficult to control. The closed reactors, on the other hand can be designed and operated in order to maintain the optimum conditions for the process. but such systems are invariably cost intensive and are. in general. inappropriate for most pig farms. The aerated static pile composting has been shown to be a reliable system (Keeley and Skipper. 1988) requiring minimal operational inputs.

5 m3 aerated static pile compost trials were carried out with untreated saw dust as the bulking agent. The results of performance of composting trials is discussed and the feasibility of nutrient recovery through composting is demonstrated.

MATERIALS AND METHODS

Substrate

The solids used in the composting trials were collected from the overflow of a rotary screen which separated the solids from the piggery effluent. The compost piles were constructed on the same day in order to prevent degradation before the trials.

Untreated saw dust was used to increase the porosity of the substrate. The moisture content of the saw dust was adjusted by adding water to achieve the required final moisture content of the substrate-bulking agent mixture.

Aerobic thennophilic composting 91

Construction of static pile

A piping manifold made up of PVC header and lateral pipes was placed in a concrete floor with appropriate slope for drainage. The 2.5 m long laterals with a diameter of 20 mm had 20 orifices of 2 mm each.

The aeration piping was covered with a plastic mesh and a layer of wood chips of 10 cm thickness was placed to facilitate even distribution of air through the pile. Type K thermocouples were used to measure the temperature. The progression of temperature build up was recorded using a Honeywell Versaprint multipoint recorder.

Ana!ytical methods

The total organic carbon was measured according to the procedure set out in Bolan and Hedley (1987).

The total Nitrogen and Phosphorus were determined by digesting the samples according to McKenzie and Wallace (1954). The total Nitrogen was measured by a colorimetric method, using a Technicon Autoanalyser. The phosphorus content was determined using vanadomolybdate method (AOAC, 1975).

The Most Probable Number (MPN) and Streptococci were measured following the procedure developed by Bogoni (1988).

RESULTS AND DISCUSSION

The composting trials were carried out using different substrate to bulking agent ratios and aeration rates. These are summarized in Table 2. Aeration was provided by a blower. Six thermocouples were positioned in the bottom, middle and top layers within the pile and samples were withdrawn from top and middle layers using a concentric pipe sample collection device which could be inserted to the desired position in the pile. The location of thermocouples and sampling points is shown in Figure I while Figure 2 shows the 'on-off timer configuration for aeration and temperature measurement.

Table 2. Aeration and waste-sawdust ratio for various trials

Trial # Aeration Wute-Sawdult ratio (%)

f---1 48 hrs continuous 50:50

followed by 10 mln/hr

2 48 hrs continuous 50:50 followed by 10 mln/hr

3 24 hrs continuous 50:50 followed by 10 mln/hr

4 10 mln/hr 50:50

5 10 mln/hr 25:75

6 10 mln/hr 75:25

In addition to temperature, total nitrogen, total phosphorus, total organic carbon, total solids and volatile solids were monitored initially every day up to 10 days and every 5 days thereafter until the completion of the trial, that is 21 days. The sampling points were located at 15 cm and 75 cm from the top.

92

Phese

Supply

AC

S. M. RAO BHAMIDlMARRI and S. P. PANDEY

• S2 • T4

Figure I. PositIon ofthermocouple and sampling pomts

Air Timer

Pause Timer

Recorder Timer

-Temperature Recorder

Figure 2. Timer configuration for the 'on-ofr regime of the aeration and the temperature measurement Mode of limer shown: Air supply.

80r-----------------------------------~

70

60 u ., 50 ... ::> -l:?40 OJ a. E ~ 30

20

5 7 9 11 13 15 17 19 21 23 time ( days)

Figure 3. Temperature profiles for small scale composting trial.

Aerobic thermophilic composting 93

Temperature development

The temperature development during the trial is presented in Figure 3. The temperature increased rapidly in the initial stages reaching around 700e within 3 to 4 days with 24 hours continuous aeration followed by aeration for 10 minutes every hour for the rest of the composting cycle. The temperature at location T I increased only up to 520 e by day 3, and decreased rapidly. This was primarily because of drainage and increased moisture at that location to a level when thermophilic activity could not be sustained. In some cases, the temperature of the top layers reached 800C and this temperature did not decrease over the entire cycle. Such high temperatures prevent re-establishment of fungi, actinomycetes and other soil organisms which are reported to be important in the production of humic materials (Biddlestone and Gray, 1985). However, the impact of this on the overall compost quality is unknown and needs further investigation.

Nutrients

The concentrations of nitrogen and phosphorus measured over the composting period showed that up to 79% of total nitrogen was conserved while there was no significant change in the phosphorus concentration. The average nutrient concentrations are shown in Table 3. In the case of sewage sludge, most of the nitrogen was reported to be lost as ammonia (Stentiford, 1987). Up to half of nitrogen loss was reported by Bogoni (1988) during the composting of sewage sludge mixed with woodchips. The high level of nitrogen conservation in this study appears to be mainly because of the sawdust which has a high ammonia retention capacity. There was no significant change in phosphorus concentrations and these results are similar to those reported in the literature (Bogoni, 1988). The observed organic carbon loss on a dry basis was less than expected. This was primarily because the bulking agent has a very high organic carbon content and therefore, the decrease in the organic carbon of the mixture is small.

Table 3. Nutrient analysis of substrate and compost

Sample

Fresh Manure

Compost

10000000

~1000000 c '" 8 100000 ] ~ 10000 ... u i

1-'-

5

TN TP mg/g mg/g

16.52 7.7

6.53 3.9

Enterococci -0- MPN

40 1~ 20 time (days)

Figure 4. Most probable number and streptococci in the composted pig waste.

25

94 S. M. RAO BHAMlDIMARRI and S. P. PANDEY

Microbjal counts

The microbial counts of Streptococci and MPN are presented in Figure 4. Streptococci decreased by four orders of magnitude while the MPN showed three orders of magnitude decline. The high temperatures of the pile for prolonged periods are expected to decrease the bacterial counts to levels lower than those observed. The high values of MPN indicate that there are certain spore fonners which survive the composting process. Further work on the nature of these organisms is needed to determine the need and method for their inactivation.

CONCLUSION

Piggery solid wastes are nutrient rich fibrous material readily amenable to aerobic composting. This study demonstrates that sawdust is the appropriate bulking material for piggery solid composting as it has a higher ammonia retention capacity in addition to providing an additional carbon source. Thennophilic composting reduces the microbial counts. including the Enterococci significantly. primarily because of the sustained thermophilic activity facilitated by the most suitable nutrient ratios present in the piggery solids sawdust mixtures.

REFERENCE

AOAC (Association of Official Agricultural Chemists) (1975). Official Analysis. 12th Edition; Association of Official Agricultural Chemists; Washington. DC. U.S.A.

APHA (American Public Health ASSOCIation) (1986). Standard Methods for the Examination of Water and Wastewater. 16th ed. American Public Health Association. Washington. DC. U.S.A.

Biddlestone. A. J. and Gray. K. R. (1985). Composting.In. Comprehensive Biotechnology. Vo!. 4. Robinson. C. W. and Howell. J. A. (Eds.) Pergamon Press Ltd.

Bogoni. C. (1988). Sewage Sludge Disposal : the Composting Option. M. Tech. thesis. Massey University. Palmerston Nonh. New Zealand.

Bolan. N. S. and Hedley. M. J. (1987). Selected methods of analysis. Course: Analytical TechnIques. Depanment of Soil Science. Massey University. Palmerston Nonh. New Zealand.

Finstein. M. S. and Miller. F. C. (1985). Principles of compostmg leading to maximization of decomposition rate. odor control. and cost effectiveness. pp. 13·26. In: Composting of Agricultural alld Other Wastes. Gasser. J. K. R. (Ed.). Els. App!. Sci. Pub!. London and New York.

Gotaas. H. B. (1956). Composting·Sanitary Disposal and Reclamation of Organic Wastes. Published by the WHO. Geneva. Switzerland.

Keeley. G. M. and Skipper. J. L. (1988). The use of aerobic thermophilic composting for the stabilization of primary meat waste solids. pp. 120-131. In: Altemative Waste Treatmel/t Systems. Bhamidlmarri. S. M. R. (Ed). Els. App!. Sci. Pub!. London and New York.

Stentiford. E. 1. (1987). Recent development in composting. pp. 52·60. In: Compost: Production. Quality and Use. De Benoldi. M. et al. (eds.). Els. Appl Sci. Pub!. London and New York.

Vanderholm. D. H. (1984). Agricultural Waste Mal/ual. New Zealand Agricultural Engineering InstItute. Lincoln University. Canterbury. New Zealand.

Warbunon. D. J. (1980). Handling. storage and treatment of plggery waste ; In: Generating Profit from the Pig Herd. Massey University. Palmerston Nonh. New Zealand.

Wilson. G. B. (1983). Forced aeration composting. War. Sci. Tech. IS(I). 169·180.