Novel Nutrient Recovery Process from Wastewater Treatment Plants

Abstract

Small scale wastewater treatment plants (WWTPs) tend to have low efficiencies of nutrient recapture, especially of phosphorus (P). Phosphorus removal performed by biological accumulation steps is directly opposed to the hydrolytic nature of anaerobic digestion. The use of both processes in WWTPs results in a high load of nutrients in the digestate, which can be problematic during long-term operation of the plant and can increase nutrient loading into the hydrologic systems where they discharge. This research focused on the development of an integrated system to allow for the efficient release of phosphorus from thickened sludge and its subsequent recapture. Through the implementation of a two-stage anaerobic digestion, the effluent can be digested and subsequently be treated in intermediate reactors for solid separation and nutrient recapture. This system was scaled up into a pilot plant model with a continuous stirred tank reactor (CSTR) thermophilic fermenter, a sequencing batch reactor for P precipitation, and an upflow anaerobic sludge blanket (UASB) digester to model large-scale municipal wastewater treatment. This system has the capacity of producing a low-odor low-organic load liquid effluent, as well as value-added commodities such as biogas and high-purity P-bearing minerals. However, further optimization and scaling need to be performed to establish a completely continuous and economically feasible system.