Life cycle thinking applied to phytoremediation of dairy wastewater using aquatic macrophytes for treatment and biomass production

Abstract

The conventional way of treating effluents is expensive. So, it is common to find small and medium-sized dairy industries that don’t treat their wastewater, which contains high levels of organic and inorganic matter. This study used aquatic macrophytes in constructed wetlands (CWets) and CWets associated in series, to evaluate the treatment of dairy effluents and the cycling of nutrients (nitrogen and phosphorus), as well as the environmental burdens for the use of post-treatment aquatic biomass. The macrophytes tested were Cyperus articulatus, Eichhornia crassipes, Eleocharis interstincta and Typha domingensis. The phytoremediation efficiency was evaluated by considering the following physicochemical parameters: Chemical Oxygen Demand, Biochemical Oxygen Demand, Total Solids, Dissolved Solids, Suspended Solids, Sedimentable Solids, pH, Nitrogen, Phosphorus and weight of aquatic macrophytes. Life Cycle Assessment method allowed to compare different scenarios for biomass (C. articulatus) destination after the treatment: (S1) animal feed and (S2) biogas/biofertilizer production, considering 1 m3 of treated effluent as the functional unit. The research showed that all chosen macrophytes reduced BOD by more than 70% in the CWets. fFor the 4-day hydraulic retention time, the Cyperus articulatus was the aquatic macrophyte with the best global performance in organic load reduction. Subsequently, the CWets in series reached average reductions of 75% for tP and 58% for tN using E. crassipes. Regarding the use of post-treatment biomass, S1 was the most favorable alternative for the mitigation of greenhouse gas emissions and eutrophication. For the impact categories of ozone depletion, terrestrial acidification, and cumulative exergy demand, there were no statistical differences between the scenarios S1 and S2. The aquatic macrophytes can be used in the treatment and cycling of nutrients of dairy effluent, with enhanced results when combined or arranged in CWets in series.