Use of lignite fly ash as an additive in alkaline stabilisation and pasteurisation of wastewater sludge

摘要

In this study, the possibility of using lignite fly ash in low doses for reducing the pathogen levels in wastewater sludge was investigated. The results showed that using fly ash alone in doses of 40 percent, 80 percent and 120 percent (on a dry weight basis), did not produce an alkaline environment for an efficient removal of pathogens. However, using fly ash in conjunction with the minimum amount of quicklime may act as an effective way of fecal coliform removal in both alkaline stabilisation and pasteurisation processes. It was shown that using fly ash in doses of 80 percent and 120 percent in alkaline stabilisation and pasteurisation processes prevented the pH decays and regrowth of pathogens during 60 days of storage period. The results of the study confirmed that alkaline pasteurisation process produces a product which is more resistant to pH decays and regrowth of fecal coliforms compared to that of alkaline stabilisation. Consequently, the overall results of this study indicated that the minimum lime and fly ash dosages required to generate a Class B biosolid were 10 - 15 percent and 80 percent, respectively. On the other hand, heating sludge to 50 deg C prior to the addition of 10 - 15 percent quicklime and 80 percent fly ash followed by further heating to 70 deg C and then sustaining at this temperature for 30 minutes were sufficient to generate a Class A biosolid.