Waste stabilisation pond sewage treatment system : its appropriateness to a regional city of Thailand

An investigation of Khon Kaen WSP revealed that the WSP was more appropriate to the Thai regional cities' situation in both sewage treatment objective and socio-economic context. The WSP was capable of treating raw sewage meeting Thailand's effluent standard in BOD, pH, total coliform and faecal coliform counts, except TSS. Sunlight, temperature, pH, phosphate, nitrate, retention time, pond geometry, pond location towards the wind direction and removal of algal mats appeared to be major factors influencing the biological pollutant degradation activities inside the ponds. Offensive odour, as a main public complaint about the plant, resulted from the abundance of floating algal mats. Some conventional WSP design equations were found to be less effective in effluent quality prediction compared with the actual pond performance. The result of the analysis of some of the contemporarily designed BOD loading equations applied to this plant showed that such equations were less appropriate to the Khon Kaen city environment. The actual BOD loading-removal linear equation investigated from this existing plant could be the best method for future WSP development in this region. The plant, with low costs of construction, operation and maintenance, was found to be cost-effective and suited to Khon Kaen city conditions. The plant required more operators and the present workers need additional training and experiences. Supplying the operators with equipment for removing algal mats appeared to reduce offensive odours and increased pond performance. Due to TSS level in the final discharge being over the country's standard, initiating any measure for decreasing TSS would be necessary for this plant.