No abstract

A SULPHUS biotrickling filter (BTF) and an ACTUS polishing activated carbon filter (ACF) were used at a wastewater treatment plant to treat 2,432 m·h of air extracted from sewage sludge processes. The project is part of Thames Water's strategy to reduce customer odour impact and, in this case, is designed to achieve a maximum discharge concentration of 1,000 ou·m. The odour and hydrogen sulphide concentration in the input air was more influenced by the operation of the sludge holding tank mixers than by ambient temperature. Phosphorus was found to be limiting the performance of the BTF during peak conditions, hence requiring additional nutrient supply. Olfactometry and pollutant measurements demonstrated that during the high rate of change of intermittent odour concentrations the ACF was required to reach compliant stack values. The two stage unit outperformed design criteria, with 139 ou·m measured after 11 months of operation. At peak conditions and even at very low temperatures, the nutrient addition considerably increased the performance of the BTF, extending the time before activated carbon replacement over the one year design time. During baseline operation, the BTF achieved values between 266-1,647 ou·m even during a 6 day irrigation failure of the biofilm.

The whole life costs of chemical and biological phosphorus removal are comparable if the sewage contains sufficient readily biodegradable carbon (rbCOD) to stimulate biological phosphorus removal (BPR). To date, standard practice is to dose iron salts (an industrial byproduct) into the activated sludge basin. However, the cost of iron salts is increasing because the industries which produce these iron salts are closing. For this reason, biological removal is often the preferred option in the UK when the sewage contains an industrial source of rbCOD. The design of these new wastewater treatment plants (WWTPs) has to take into account the type and amount of carbon available and the operation of industry in question.