Abstract:
The study investigated changes of certain bacterial indicators, copper and zinc in affluence and effluence from 5 different wastewater treatment systems commonly used in pig farms in Thailand. The systems included (1) biogas system, which consisted of biogas BAU, cover lagoon, and CARMATEC system and (2) ponding system, which consisted of anaerobic filter and stabilizing pond. Samples were collected from 5 pig farms for each treatment system during August-October 2005 and February-April 2006 in Ratchaburi province. The results showed that wastewater affluence from swine farms that used biogas systems had significantly (p < 0.05) higher total bacterial count, coliform count, fecal coliform count and concentration of copper and zinc than those that used ponding systems. Total bacterial count, coliform count, fecal coliform count and concentration of copper and zinc of waste water effluence of all studied systems were not significantly different. However, wastewater effluence had an average coliform count of 10[superscript 3] -10 [superscript 5] MPN/100 ml, an average copper concentration of 0.02-0.28 ppm., and an average zinc concentration of 0.49-2.46 ppm. Data from this study also revealed that most of the wastewater effluence, which passed the minimum requirement of wastewater discharge declared by the environment protection agency, were contained not only high number of bacterial indicators count, especially, coliform and fecal coliform count, but also higher amount of copper and zinc than the allowable level of copper and zinc concentration in surface water used for agricultural purposes. In conclusion, wastewater effluence of which BOD, COD, TKN and SS met the minimum requirement of wastewater discharge by law might still post a public health hazard due to a high number of bacterial indicators count and high concentration of copper and zinc.