Life cycle assessment comparison of industrial effluent management strategies

A process model was analysed with life cycle assessment (LCA) to evaluate the environmental tradeoffs of fourteen process alternatives treating a pulp and paper effluent with high levels of chemical oxygen demand (COD) and adsorbable organic halides (AOX). The process alternatives were constructed from six unit processes: dissolved air flotation, clarification, activated sludge, upflow anaerobic sludge blanket reactor, ultrafiltration and reverse osmosis (RO) treatment. The tradeoffs between environmental impact categories were investigated, focussing on eutrophication, freshwater aquatic ecotoxicity (FWAE), greenhouse gas (GHG) emissions and water extraction. For each configuration, the water recovery and contaminant removal effectiveness were compared against GHG emissions. the most intense treatment option was able to reduce AOX by 99.6% and COD by 99.9%, the FWAE and eutrophication categories had a reduction of only 98.6% and 94.2%, respectively. The GHG emissions were heavily influenced by sludge landfilling contributing between 39% and 71% of overall emissions, with electricity production becoming significant as treatment intensity increased. The alternatives considered were able to produce a recycled water stream composed of 3%–100% of treated effluent. Configurations using RO produced effluent with sufficient quality to be used in recycled water applications without dilution. Configurations with ultrafiltration as the highest level of treatment could produce a recycled water stream composed of 35%–81% treated effluent. Contaminant discharge impacts, water recovery and GHG emissions did not have a single optimal configuration. The study demonstrates the ability of this model to identify marginal tradeoffs between environmental impacts.