Recovery and valorisation of cellulose from sewage: The road to circularity
Marcelis, P. and Wessels, C., CirTec B.V., The Netherlands
(free)
Abstract
At present, the UK wastewater treatment industry is facing an increasing number of challenges from a variety of different drivers both from a regulatory standpoint and with regards to increasing public awareness of pollution events. Such challenges include the need for a better effluent quality with low levels of phosphorus, ammonia, and total nitrogen (among others), as well as meeting this improved effluent without the need for chemical dosing or increasing site footprints. The C-TECH cyclic activated sludge technology from SFC Umwelttechnik and delivered by Trant Engineering is able to satisfy these drivers in a single treatment step. The design of this process enables the formation of macroflocs, which allow for simultaneous nitrification and denitrification, as well as the formation of PAOs (phosphorus accumulating organisms) for high rates of biological phosphorus (bio-P) removal. The C-TECH process is able to achieve effluent values of BOD:SS:TN:TP of < 10:10:10:1 mg/l respectively, with yearly average values for a particular European site of 4.7:5.2:6.6:0.8 mg/l. Installing two or more C-TECH basins in parallel allows for continuous throughput and eliminates the need for upstream buffer tanks, mixing devices, and tertiary settling tanks, which ultimately reduces the overall site footprint when compared to traditional activated sludge or sequencing batch reactor processes. The C-TECH process has had worldwide success, with more than 600 plants and up to a capacity of 600,000m3/d.
Keywords
Bio-P, cyclic activated sludge, denitrification, macroflocs, nitrification, phosphorus
Introduction
The Urban Waste Water Treatment Directive (UWWTD) states that discharges into sensitive areas which are subject to eutrophication carry additional consent limits for either of both phosphorus and nitrogen. Current limits for total nitrogen are 15mg/l N for 10,000-100,000 PE sites and 10mg/l N for greater than 100,000 PE sites and for total phosphorus are 2mg/l P for 10,000-100,000 PE sites and 1 mg/l for greater than 100,000 PE sites. However, these limits are expected to tighten in the forthcoming AMP periods with phosphorus limits decreasing to as low as 0.1mg/l. Furthermore, as shown in Figure 1, the number of sensitive areas within the UK has increased significantly since the UWWTD’s conception in 1994 and is expected to increase further. Both these factors highlight the need for water companies to invest in nutrient removal treatment processes to ensure they remain compliant in the years to come. A scarcity of available land for construction and financial constraints from Ofwat also calls for low footprint and low TOTEX solutions to be implemented for nutrient removal.
