A novel process for organic acids and nutrient recovery from municipal wastewater sludge

Abstract

In this paper, a novel process for organic acids and nutrient recovery from municipal sludge was introduced and evaluated based on laboratory-scale studies. An economical estimation for its practical application was also performed by mass balance in a full-scale plant (Q=158,000 m3 d(-1)). This novel process comprises an upflow sludge blanket-type high performance elutriated acid fermenter (5d of SRT) for organic acids recovery followed by an upflow-type crystallisation (3 h of HRT) reactor using waste lime for nutrient recovery. In the system, the fermenter is characterised by thermophilic (55 degrees C) and alkaline conditions (pH 9), contributing to higher hydrolysis/acidogenesis (0.18 g VFA(COD) g(-1) VSS(COD), 63.3% of VFA(COD)/COD produced, based on sludge characteristics of the rainy season) and pathogen-free stabilised sludge production. It also provides the optimal condition for the following crystallisation reactor. In the process, the waste lime, which is an industrial waste, can be used for pH control and cation (Ca and Mg) sources for crystallisation reaction. A cost estimation for full-scale application demonstrates that this process has economic benefits (about 67 dollars per m3 of wastewater except for the energy expense) even in the rainy season.