The National Investigations Programme 2020-21 Mechanisms for Removal: PRESENTATION ONLY

Davies, S., Dai, Z. and Herron, D., Aqua Enviro, UK


A nitrogen and phosphorus mass balance investigation was conducted on four wastewater treatment plants that vary from the discharge consent, the population equivalent and the onsite sludge treatment, for identifying the potential nutrient recovery opportunities.

The mass balances suggested that 30-70% of the influent nutrient remained in the final effluent and was discharged back to the environment. Meanwhile, approximately two-thirds of the influent phosphorus and one-third of influent nitrogen were captured in the sludge. During the subsequent sludge treatment, 20-30% of the influent nitrogen and 35-55% of the influent phosphorus could end up in the filtrates and centrates which will be recirculated back to the head of the work, and 7-14% of the influent nitrogen and 19-30% of the influent phosphorus could be kept in the digested sludge (known as biosolid).

Nutrient recovery has been conducted through fertilizer recovery from centrate and spreading biosolid on land. Presumably, the ferric dosing and enhanced biological nutrient removal (EBPR) could potentially capture more nutrient into the sludge during the wastewater treatment and thereby lead to a greater extent of nutrient recovery. The impact of the addition of the two approaches to the existing treatment train on the mass balance was investigated via modelling (GPS-X 7.0). Results suggested that EBPR would improve the recoverable and soluble phosphate loading in the centrates of the sludge treatment but barely affects the digested sludge, and ferric dosing minimally impacted the centrate but elevated the phosphorous content in the biosolid because more phosphate was bounded as ferric phosphate and was remained in the particulate fraction throughout the whole treatment process. Meanwhile, the nitrogen mass balance was slightly impacted.

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