Impact of graphene oxide addition on pharmaceuticals removal in anaerobic membrane bioreactor.

The addition of conductive materials to the anaerobic digestion bioreactor was suggested to enhance microbial activity. In the present work, an anaerobic membrane bioreactor treating municipal wastewater was operated for 385 days. The impact of different graphene oxide concentrations on the removal target pharmaceuticals and microbial community dynamics was investigated. The addition of graphene oxide did not impact the reactor stability, whereas the removals of antibiotics (e.g., trimethoprim and metronidazole) were enhanced. A shift in the microbial community was detected after the addition of 50-900 mg L-1 of graphene oxide, with the proliferation hydrogenotrophic methanogens. The proliferation of syntrophic microorganisms may indicate interactions via direct interspecific electron transfer. The obtained results suggest that the addition of graphene oxide at low mg L-1 concentrations to an anaerobic membrane bioreactor may be considered to improve the removal of antibiotics from municipal wastewater.

Enhanced methane production kinetics by graphene oxide in fed-batch tests.

The study aims to prove that the addition of graphene oxide (GO) improves anaerobic digestion (AD) kinetic performance. Classical batch tests were modified to a fed-batch strategy at four GO levels while using two substrates (glucose and microcrystalline cellulose (MCC)). First-order and modified Gompertz models were respectively applied to evaluate the kinetic performance. The results showed significantly (p < 0.05) improved kinetic from the third refeeding step for both substrates. 20 mg GO per g of volatile solids (VS) led to an increase of up to 210% for the first-order rate constant (k) and up to 120% for maximum biochemical methane potential (BMP) rate (RMAX) compared to control for glucose and MCC, respectively. The findings of this work suggest the implementation of GO in continuously operated systems to accelerate the AD process.

A microsieve-based filtration process for combined sewer overflow treatment with nutrient control: Modeling and experimental studies.

Combined sewer overflows contain a highly variable, wide range of contaminants, both in particulate and soluble form, making conventional water treatment processes unable to offer adequate public health protection. In this study, an integrated treatment process designed to simultaneously remove typical combined sewer overflow pollutants (suspended solids, chemical oxygen depends, turbidity) in conjunction with nutrient (nitrogen and phosphorus), was developed. The removal of particulates as well as dissolved nitrogen and phosphorus was achieved by first adsorbing soluble pollutants on zeolite and powdered activated carbon, and subsequently applying filtration carried out by polymer-enhanced microsieving. Laboratory experiments were designed using design-of-experiment techniques and carried out to assess the effects of the various treatment variables (cationic polymer, zeolite, powder activated carbon and microsieve size) in the designed combinations. A response surface model was fitted to the experimental dataset in order to capture and describe the non-linear relationships between treatment variables and treatment objectives. Finally, an optimization study was carried out using Pareto analysis showing that cationic polymer, zeolite, and powdered activated carbon, followed by fine mesh microsieving, worked synergistically in the integrated treatment process. Several optimal process conditions emerged, in particular, a treatment combination consisting of 1.1 mg/L of the cationic polymer, 250 mg/L of zeolite, 5 mg/L of powdered activated carbon, and a 370 µm mesh size. Under this condition, expected performance would be reductions of 72%, 56%, 35%, and 75% for turbidity, total Kjeldahl nitrogen, total chemical oxygen demand, and total phosphorous, respectively. The findings presented in this paper demonstrate the possibility of achieving multiple treatment objectives in a single and integrated treatment step, hence providing municipalities with viable treatment options where the issues of combined sewer overflow and nutrient management are simultaneously tackled.