THE IMPACT OF PIGGERY SLURRY ADDITION ON MESOPHILIC ANAEROBIC DIGESTION ACCLIMATISED TO BREWERY WASTEWATER

摘要

The main objective of this research was the assessment of anaerobic co-digestion of piggery wastes with waste-streams other than animal wastes, for the maximisation of methane production. The maximisation of methane production makes the process more cost-efficient for farmers; the digesters will be in position to accept other waste streams, thus allowing the digesters to operate with larger amounts of wastes. At this stage of the research, piggery wastes were introduced to batch digesters treating brewery wastes. This paper presents the setup and up-to-date results of the experiments, the problems encountered, and the main conclusions reached. The parameters monitored regularly were pH, electrical conductivity, total solids (TS), volatile solids (VS) and chemical oxygen demand (COD). Parameters monitored periodically were methane (CH_4), carbon dioxide (CO_2), hydrogen sulphide (H_2S) in the gas produced, ammonia (NH_3) and ammonium ion (NH_4~+) in the liquid (slurry) content of the digester. The feed added to the digester was regularly monitored for TS, VS, COD, pH and conductivity. When new batches of wastes were used, the additional parameters of BOD, metals (sodium, potassium, cadmium, chromium, copper, lead, nickel and zinc) and ammonia/ammonium were measured, for the complete qualitative assessment of the waste. The particular parameters have been chosen for monitoring, due to (i) their relevance with anaerobic biodegradation, (ii) indication of the progress of the digestion (COD, TOC, TS, VS), and (iii) because of the impact that particular parameters could have on the process (pH, conductivity as indication of salinity and ammonia/ammonium ions). In comparison to the untreated pig waste added to the digester, the COD reduction obtained after 220 days of operation was 13.5%, the TS and VS reduction was 58.6% and 25.8% respectively. Based on the VS destruction, the expected methane production from this VS destruction is 1405 ml CH_4using the methane productivity of 500 ml/g. Maximum methane measured was 61.6%, much lower than theoretical. This difference could be due that not all VS are converted to methane. Consequently, the VS (and therefore TS) are accumulating in the digester, resulting to the increase in the solids with time. Conductivity in the digesters increased from 5.29 mS/cm before the addition of pig waste and to around 16.50 mS/cm, which can have negative impact to the process. Increase was also observed for pH from 7.05 to 8.13. Parameters that need further investigation are loading rates, pH and temperature influence to the particular system.