Abstract
The rapid increase in the population is expected to result in the approaching of design capacity for many US wastewater treatment plants (WWTPs) over the next decade. WWTPs treat both municipal and industrial wastewater influents, resulting in the production of biosolids after digestion. Biogas, a potential recovered alternative energy source, is also produced as an output from successful anaerobic digestion. More than 7M of dry tons/year of biosolids produced in the US are most often disposed in either landfills or land-applied (~80%). These options are becoming more challenging to implement due to increases in transportation costs and tipping fees, decreases in the availability of landfill/landfarm space, and most importantly, increased regulations. This situation is strongly encouraging WWTPs to find alternatives for the disposal of biosolids. Developing alternative management/disposal options for biosolids are evolving. One of the most attractive alternative option from a sustainability perspective are biorefineries (converts waste to commercial products), which are a fast-growing option given the push toward circular urban source economies (little to no waste generation). Anaerobic digestion has been widely applied in WWTPs to reduce the volume of activated sludge due to its low energy requirements, effective handling of fluctuations due to organic loading rate, relative flexibility with temperature and pH changes, and since biogas is produced that can be transformed into energy. Various pretreatment methods for waste sludges prior to digestion that have been studied to reduce solids production and increase the energetic content of the biogas are presented and discussed. Solids handling and management, which comprises ~60% of the operational cost of a WWTP, is estimated to save more than $100 M annually by achieving at least 20% reduction in the annual production of biosolids within the US. This review incorporates an assessment of various pretreatment methods to optimize the anaerobic digestion of waste sludges with a focus on maximizing both biosolids reduction and biogas quality.
Highlights
Wastewater treatment plants (WWTP) are designed to treat municipal and industrial wastewater influents to lower the ecological risks associated with discharging the treated effluents into receiving water sources
In selecting an optimal pretreatment process, the costs associated with the additional treatment/handling, additional process equipment operation and management (O&M), overall energy requirements, capital investment, and the influent sludge characteristics, such as the organic loading rate (OLR), Total Organic Carbon (TOC), COD, working temperature, and pH all need to be considered for the optimized selection and design of a candidate pretreatment system
Biosolids handling is a major concern for the WWTP operators which can be alleviated by more efficient removal of total solids within the Anaerobic digestion digestion (AD)
Summary
Bimi Shrestha 1 , Rafael Hernandez 1 , Dhan Lord B. Fortela 1 , Wayne Sharp 2 , Andrei Chistoserdov 3 , Daniel Gang 2 , Emmanuel Revellame 4 , William Holmes 5 and Mark E. Received: 18 November 2020; Accepted: 18 December 2020; Published: 21 December 2020
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