THESIS
2020
xx, 163 pages : illustrations (some color) ; 30 cm
Abstract
Food waste (FW) management is a worldwide environmental issue. Diversion of FW by using
Food Waste Disposers (FWDs) into the sewer system is considered potentially viable for
relieving the burden of municipal solid waste (MSW) management. However, the feasibility of
such practice is still under debate due to significant concerns over the impacts of adding FW
into the sewer system and the downstream wastewater treatment plants (WWTPs). In this
context, the present study has systematically investigated local FW characterization, FW
transformation during wastewater treatment, and potential implications of the FW addition on
sewer processes and WWTP operation. Main contents and results are as follows:
Firstly, FW characterization is a key issue and needed to be conducted in advance...[
Read more ]
Food waste (FW) management is a worldwide environmental issue. Diversion of FW by using
Food Waste Disposers (FWDs) into the sewer system is considered potentially viable for
relieving the burden of municipal solid waste (MSW) management. However, the feasibility of
such practice is still under debate due to significant concerns over the impacts of adding FW
into the sewer system and the downstream wastewater treatment plants (WWTPs). In this
context, the present study has systematically investigated local FW characterization, FW
transformation during wastewater treatment, and potential implications of the FW addition on
sewer processes and WWTP operation. Main contents and results are as follows:
Firstly, FW characterization is a key issue and needed to be conducted in advance to lay a
foundation for this study. A one-year physicochemical analysis of representative samples
suggested that one gram wet weight of FW contains 160 mg solids, 230 mg chemical oxygen
demand (COD), 3 mg nitrogen and 1.2 mg phosphorus on average. Moreover, Hong Kong
household FW typically consists of 50% fruit, 20% vegetables, 20% starchy food and 10% meat.
Theoretical estimations indicate the addition of FW into wastewater would certainly increase
the pollutant loading on the WWTPs, but also has energy recovery potential.
Secondly, the impacts of the FW addition on the sewer biofilm were evaluated via pilot-scale
gravity sewers. In a gravity sewer system, the sewer biofilm properties change with long-term
FW addition, resulting in a greater thickness (by 32%), an increased dry density (by 13%), and
more extracellular polymeric substance (by 141%). The thicker and denser biofilm limits
oxygen diffusion, enlarges the anaerobic area in the sewer biofilm, promotes an increase in the
sulfate-reducing bacteria (SRB) population, and enhances the sulfide production potential.
Moreover, the impacts of the FW addition on the sewer processes were examined by a lab-scale
sewer reactor system under low and high sulfate conditions (40 and 160 mg S/L). The long-term
monitoring of the system revealed that the FW addition has little impact on sulfide
production, but methane production was enhanced by up to 62% under a low sulfate condition,
whereas improvements of sulfide and methane production were around 39% and 44% by dosing
FW under a high sulfate condition. The addition of FW significantly promoted the accumulation
of methanogenic archaea (MA) and altered the spatial distributions of SRB and MA in the sewer
biofilms.
Further, a plant-wide COD-based transformation model was established by using local data to
evaluate the conversion of FW, the energy balance and the overall operational cost in WWTPs,
in sludge treatment and in MSW management. The WWTPs can remove about 78% of solids
and 58% of COD in FW. The FW addition however has limited impact on the treatment capacity,
effluent quality and sludge production in WWTPs in the short term. The increases in energy
consumption and operational cost are dependent on the treatment processes and the FWDs
penetration rates, while the MSW treatment can benefit from the use of FWDs.
This research has shed light on the overall impacts of diverting FW into the sewer system, and
the results provides important information for future research and policy decision-making in
FW management.
Post a Comment