Introduction

Deforestation results into reduction in the fertility of the agricultural land by erosion of soil. The dung and firewood energy is detrimental for living being due to smoke which leads to air pollution. Due to shortage of coal and petroleum, supply of fuel throughout the world is a matter of concern for the future generation eco-friendly substitute of energy. The combustion of these products and pollution of environment led to research in different corners to find the renewable energy resources like solar energy, wind energy, different thermal and hydro sources of energy and biogas. But, biogas is unique from other renewable energies due to its characteristics of collecting organic wastes, controlling and using and at the same time producing fertilizer for agricultural practices (Hamelinck et al., 2005). The production of methane from varieties of biological organic wastes through fermentation technology is rising throughout the world and is well thought-out feasible solution in current scenario (Appels et al., 2008). It is economical and environment friendly technology. In respect of energy output/input ratio, this technology is the most efficient as compared to all other technologies of energy production through biological or thermo-chemical routes of energy conversion processes (Gerardi, 2003: Deublein et al.,2011). In India, biogas production is an age old technology, where cow dung is mainly used for this purpose. However, piggery excreta has not considered for this purpose so far. The pig contribute 2.01% (BAH & FS, 2015) in the total Indian livestock population (10.29 million) but the piggery waste neither utilized as manure in agriculture field nor used to produce biogas as compared to other livestock waste. The pig dung simply washed out in the drain in our country, which is totally wastage of organic matter having good amount of nitrogen and phosphorus. In opinion of many workers, biogas production from piggery excreta is comparatively difficult. Conditioning of pig manure for efficient feedstock loading to the biogas digester may be achieved by different ways and means like increasing C: N ratio, decreasing ammonical nitrogen production, decreasing hydrogen sulphide content, adjusting the desirable pH etc. Therefore, carbonization, dilution and buffering of pig excreta may be effective conditioning techniques for efficient biogas production at swine establishments. Considering the above facts, the present study was undertaken to optimize the different variables for efficient biogas production from pig manure.

Materials and Methods

Eight numbers of pooled fresh pig manure sample, was collected from crossbreed (Landrace × Desi) pigs of Swine Production Farm, Livestock Production and Management Section, Indian Veterinary Research Institute (IVRI), Izatnagar, Bareilly. All the pigs were vaccinated and de-wormed as per farm schedule. Requisite quantities of fresh pig manure were sampled for analysis.

The proximate composition of fresh pig dung was estimated as per Association of Official Analytical Chemist (2000). Percent organic matter in the samples was estimated by deducting total ash (%) from hundred (OM = 100 – Total ash). Calcium in faecal sample was estimated from the mineral extract following procedure of Talapatra et al. (1940). The phosphorus content of faecal sample was estimated from the mineral extract as per AOAC (2000) using UV visible spectrophotometer UV-1101, Precision Biotek Instruments Pvt. Ltd, New Delhi. Ammonical nitrogen content of the faecal sample was determined by the method suggested by Sastry et al.(1999). pH and electrical conductivity (EC) of pig manure was estimated from the fresh pig manure (without addition of diluted acid) with the help of digital pH meter. The total carbon was calculated from total organic matter value using the conventional Van- Bemelem Factor of 1.724 (Navarro et al., 1993). Carbon: Nitrogen ratio was calculated from two values obtained in proximate composition of the faecal sample (Total Carbon = Organic Matter (OM)/1.724; Total Nitrogen= Crude Protein (CP)/ 6.25; C: N Ratio = Total carbon/ Total nitrogen). The bacterial load was calculated using Pour Plate Technique (Miles and Misra, 1938). The number of oocysts per field was counted as per Stoll’s dilution method (Soulsby, 1982). The collected and calculated data from this experiment was compared with cow dung composition for identification of primary limiting factors of pig manure for biogas production.

Results and Discussions

Data obtained from the composition of fresh pig manure were analyzed and reasons for poor biogas production probability were ascertained after comparing pig manure with cattle dung composition (Kiyasudeen et al., 2015 and Tu et al., 2008). The detail proximate composition of fresh pig manure used in this experiment and the composition of cow dung as per literature has been mentioned in Table 1.

Table 1: Composition of fresh pig manure and cow dung

*Indicates the values calculated on TS basis

The moisture and total solid percentage of fresh pig manure was 79.27% and 19.73% respectively. The volatile solid percentage (also called as organic matter) was 82.04% in the pig manure which directly contributing to total carbon of the biomass. The ash, crude fiber and ether extract percentage were 17.96, 13.96 and 4.45 respectively. Similarly the calcium and phosphorus in pig manure was 0.33% and 0.89%. Many researchers (Nohra et al., 2003; Zhu et al., 2004; Ogunwande et al., 2013 and Lin et al., 2015) had already estimated the composition of fresh pig manure in their experiments and the findings on different proximate components of fresh pig manure of this experiments, was very much closer to the previous findings. Comparing both the columns in Table 1, the major shortfall was found in terms of C: N ratio, ammonical nitrogen and pH in pig manure for efficient biogas production. The C: N ratio in pig manure was 14:1. As pig excreta has lower level of C: N ratio, it can be conditioned by addition of some carbonaceous materials to raise the C: N ratio above 20:1, which is the desired C: N ratio for efficient biogas production (Lapp et al., 1975). Furthermore, at the time of selection of carbonaceous material one must try to maintain other constituent of the mixture undisturbed. The ammoniacal nitrogen was 2.58% in fresh pig manure. The ammonical nitrogen of pig manure was 25 % of total nitrogen estimated from Kjeldahl method on total dry mater basis. This ammoniacal nitrogen also takes part in hydroxide ion formation in atmosphere and burns plant materials when pig manure applied in its fresh state. Dilution is one of the important processes through which ammonia production can be reduced (Callaghan et al., 1999; Chandrahas et al., 2016). So, to reduce and fixing of the ammonical nitrogen during anaerobic digestion, dilution of pig excreta may be another technique for conditioning. The pH of fresh pig manure was slight acidic (6.73) which is in the range of desirable range pH for optimum biogas production, i.e. 6.5 to 7.5. However, due to break down of ammonical nitrogen during anaerobic digestion ammonium increases the pH to alkaline side and probably inhibits the biogas production. So hypothesis was, initial pH more towards acidic side, so that after conversion of ammonical nitrogen to ammonium the acidic pH could be maintained at least in the desired level, for longer duration required for uninterrupted biogas production. The pH of the pig excreta directly depends upon the CP content of the ration and processing of the feed. Therefore, addition of inorganic acid or bases to the loading mixture can achieve the desirable pH required for the optimum biogas production. The microbial consortia in fresh manure were detectable in terms of TBC and E. coli, where as no salmonella and salmonella like organism was found in fresh pig manure. The Log₁₀ value for TBC and E. coli was 6.3 and 1.8 respectively however the Log₁₀ value for TBC and E. coli count was within the normal range. No parasitic egg was detected in fresh pig manure. As the deworming protocol has been strictly followed at the swine farm and the overall hygiene and sanitation was quite good, so, the oocyte counts was nil in fresh pig manure.

Conclusion

C: N ratio, ammonical nitrogen and pH are major primary limiting factors in pig manure, which needs to be conditioned with suitable techniques of carbonization, dilution and acidification respectively for efficient biogas production.

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