Detailed LCA study of acetic acid production using microbial electrosynthesis to explore scenarios when this process could become sustainable.

No abstract

A SULPHUS biotrickling filter (BTF) and an ACTUS polishing activated carbon filter (ACF) were used at a wastewater treatment plant to treat 2,432 m·h of air extracted from sewage sludge processes. The project is part of Thames Water's strategy to reduce customer odour impact and, in this case, is designed to achieve a maximum discharge concentration of 1,000 ou·m. The odour and hydrogen sulphide concentration in the input air was more influenced by the operation of the sludge holding tank mixers than by ambient temperature. Phosphorus was found to be limiting the performance of the BTF during peak conditions, hence requiring additional nutrient supply. Olfactometry and pollutant measurements demonstrated that during the high rate of change of intermittent odour concentrations the ACF was required to reach compliant stack values. The two stage unit outperformed design criteria, with 139 ou·m measured after 11 months of operation. At peak conditions and even at very low temperatures, the nutrient addition considerably increased the performance of the BTF, extending the time before activated carbon replacement over the one year design time. During baseline operation, the BTF achieved values between 266-1,647 ou·m even during a 6 day irrigation failure of the biofilm.

Microbial electrosynthesis (MES), is an emerging technology, for sustainable wastewater treatment. The dilute acetate solution, produced via MES, must be recovered, as dilute solutions can be expensive to store and transport. The acetate is expensive and environmentally damaging to recover by heat-intensive evaporative methods, such as distillation. In pursuit of a better energy economy, a membrane separation system is simulated to raise the concentration from 1 to 30 wt%, at a hydraulic pressure of approximately 50 bar. The concentrate is then simulated to be heat dried. Reverse osmosis (RO) could rase the acetate concentration to 8 wt%. A novel adaptation of osmotically assisted reverse osmosis (OARO) is then simulated to increase the concentration from 8 to 30 wt%. The inclusion of OARO, rather than a standalone RO unit, reduces the total heat and electric power requirement by a factor of 4.3. It adds to the membrane area requirement by a factor of 6. The OARO simulations are conducted by the internal concentration polarisation (ICP) model. Before the model is used, it is fitted to OARO experimental data, obtained from the literature. Membrane structure number of 701 µm and permeability coefficient of 2.51 L/m2/h/bar are ascertained from this model fitting exercise.