Using a life cycle assessment methodology for the analysis of two treatment systems of food-processing industry wastewaters

Feasibility evaluation of wastewater treatment plants’ designs & operation strategies is nowadays done in a plant-wide perspective. Environmental concerns regarding energy consumption and sludge disposal are the main drivers to consider pre/post-treatment units in these evaluations. Existing criteria involve sludge disposal strategies and electrical energy consumption. However, there is a need to develop a systematic methodology to quantify relevant environmental indicators; comprising information of the wastewater treatment system in a life cycle perspective. Also, to identify which are the parameters that have the greatest influence on the potential environmental impacts of the systems analyzed. In this study, we present a systematic methodology for the analysis of the operation of two modern wastewater treatment technologies: Biological removal of nitrogen and organic matter by activated sludge (Scenario 1), and anaerobic removal of organic matter by a continuous stirred tank reactor (Scenario 2). Both technologies were applied to wastewater coming from a fish meals industry and a pet food industry discharging about 250 to 260 thousand cubic meters of wastewater per year. The methodology comprises three major steps: (i) Data gathering regarding wastewater characteristics and discharge, (ii) Simulation of the wastewater treatment plant’s operation by dedicated process engineering models in Matlab/Simulink, (iii) Classification and calculation of life cycle inventory data: removal efficiencies, area occupied, ancillaries consumption, energy balances, sludge production, and effluent characteristics by a Matlab script. The classified data is then fed into a generic model developed in GaBi software v.4.1 SP 8 where production of ancillaries, energy production grids, and production of fertilizers are balanced, normalized & weighted using EDIP 97. The functional unit was defined as an annual averaged volumetric person equivalent (P.E.=0,2 m3 d-1). Person equivalent is a term which results more familiar to wastewater engineers and many plant designs are expressed in that unit. The system boundaries were limited from the influent entering the wastewater treatment plant until the disposal of the effluents generated, i.e. wastewater, sludge, and biogas (for Scenario 2). Main differences between Scenario 1 & Scenario 2 were: (i) Effluent quality was 65% better when pet food wastewater was fed into the anaerobic tank whilst for fish meals wastewater was 83% better when fed into nutrients removal plant. (ii) Energy balance turned favorable only for the fish meals wastewater by anaerobic treatment producing 0,06 kWh PE-1 after energy for mixing has been utilized. (iii) Area occupied by nutrient removal tanks was bigger by at least 10 times in order of magnitude to area occupied by anaerobic tank. It was observed that in most of the weighted environmental impacts, fish meals wastewater turned into higher values. This may be due to high nitrogen concentrations in the influent which increases electricity consumption, causing higher global warming, acidification & nutrients enrichment impacts. We also noticed that sludge volumes and sludge quality were related to nitrogen and suspended solids concentrations in the influents simulated. Therefore, the sensitivities of different influent parameters over the weighted environmental impacts were investigated and quantified.