The effects of cleaning/disinfecting agents on biogas production in the anaerobic digestion of cow dung slurry

Cleaning/disinfecting agents (CDA) are compounds known to affect the growth of microbes and could have impacts on biogas production in a digester. In this study, three commonly used CDAs (harpic, hypo and izal) in livestock pens and slaughter houses were applied at different digestion stages and concentrations to cow dung (CD) slurry, with the aim of determining their effects on biogas production. Three application stages (early addition, late addition and graduated addition) were carried out for each CDA, and a CD treatment with no CDA applied was set up as the control. The results showed that application stage had different effects on the parameters of CD monitored during the digestion. Significant (p.05) effect was recorded on: temperature of izal+CD treatment, pH of harpic+CD and hypo+CD treatments, total bacterial count of hypo+CD and izal+CD treatments and biogas of harpic+CD, hypo+CD and izal+CD treatments. Early addition and increased concentration of hypo appeared toxic to anaerobic bacteria, whereas early addition of izal seemed not to affect their development. While early addition and increased concentration of harpic and hypo inhibited biogas production, the contrary was observed with izal. At the end of digestion, biogas yield (% of control) in the CDA+CD treatments ranged between 8% and 69.4% (harpic+CD), 5.4-23.5% (hypo+CD) and 16.1-52.5% (izal+CD). Among the CDAs used, hypo had the highest inhibitory effect on biogas production from CD slurry. The introduction of harpic at fourth week of digestion showed the least inhibitory effect.