Performance Evaluation of Anaerobic Forward Osmosis Membrane Bioreactor (An-FOMBR) and Anaerobic Membrane Distillation Bioreactor (An- MDBR) for Industrial Wastewater

Abstract

Water demand is increasing exponentially worldwide due to rapid urbanization and industrialization, resulting in a scarcity of clean water sources. The direct discharge of wastewater into water bodies due to the lack of wastewater treatment and reuse processes in industrial sector is resulting in environmental degradation and adverse consequences to human health. The textile industry is responsible for the discharge of dye-containing wastewater into the environment, which is generally very toxic and carcinogenic, and the discharge of these highly colored wastewater into the environment is a major threat. The effluent from conventional biological treatment technologies cannot fulfill the water reuse criteria. Hence, the combination of biological and membrane-based technologies in a hybrid system might serve as an appropriate treatment alternative. Anaerobic forward osmosis membrane bioreactor (An-FOMBR) and anaerobic membrane distillation bioreactor (An-MDBR) has stimulated growing interests for domestic and industrial wastewater reclamation having high effluent quality. However, salinity increase in An-FOMBR due to the reverse solute flux (RSF) of draw solutes ions and salt accumulation in An-MDBR due to the textile feed are the main problems for their application in textile wastewater treatment. To overcome this problem, low-cost Woven Fiber Microfiltration (WFMF) was optimized at 2 LMH in Phase 1 of this study and then coupled with An-FOMBR and An-MDBR processes for further studies. The salinity level persisted within the range of 4.3 to 7.9 mS/cm and assisted both the processes in exhibiting a continuous longterm operation in comparison with the conventional An-FOMBR and An-MDBR processes. During Phase 2 of the investigation, a laboratory-scale An-FOMBR system was set up to treat synthetic textile wastewater with a Chemical Oxygen Demand (COD) ranging from 3000 ± 150 mg/L at a temperature of 36 ± 1°C, employing Fertilizer Draw Solutes (FDSs). The study was conducted by using Ammonium Sulphate (SOA; (NH4)2SO4), Mono-ammonium Phosphate (MAP: NH4H2PO4), and Mono-potassium Phosphate (MKP; KH2PO4) each having 1M concentration which can be used for sustainable water reuse in terms of fertigation without regeneration of FDSs. For treatment of textile wastewater, color and COD removal were studied. Color removal was found to be in the range of 92.3% to 96.4% and COD removal was in between 97.8% and 99.2%, respectively. While removal efficiencies of color and COD from anaerobic bioreactor were in the range of 45.1% to 59.5% and 49.3% to 62.5%, respectively. Among the three FDS, MAP showed the best performance for 71 days with the average COD and color removal efficiencies of 98 ± 2% and 92 ± 3%, respectively with stable biogas production. Flux recovery using MAP as DS was less than 75.2% as compared to SOA 78.8% and MKP 82.8% after osmotic backwashing. Fertilizer nutrient concentrations (NH4 +1 -N, K+1, and total phosphorus) in product water were observed to be low in the initial cycles, requiring minimum dilution for direct fertigation. Moreover, inline flushing for 5 minutes also reduced the requirement for further dilution which shows the uniqueness of this study. In Phase 3 of the study, the performance of a lab-scale An-MDBR system was evaluated treating high-strength synthetic textile wastewater with a COD concentration of 3000 ± 130 mg/L. A novel hybrid process incorporating membrane distillation in a submerged anaerobic membrane bioreactor was developed and investigated at mesophilic and thermophilic temperatures. The An-MDBR process attained 99.99% inorganic salt rejection irrespective of the operating temperatures and high initial flux between 5.9 to 11.5 Liters/m2 .h (LMH) at 35-50°C. Removal efficiencies of COD and color were in the range of 40% to 69% and 43% to 74%, respectively, in an anaerobic bioreactor, whereas overall MD performance was in the range of 99 ± 0.9% for COD as well as color. Among the four temperatures, 40°C exhibited the optimum performance for 47 days with the average COD and color removal efficiencies of 99 ± 0.9%, respectively with steady biogas production. The elimination efficiency of NH4 +1 -N exhibited higher values, ranging from 89% to 93%, at mesophilic temperatures, whereas it was comparatively lower, ranging from 79% to 86%, at thermophilic temperatures, with pH levels maintained between 6.8-7.2. The concentration of PO4 -3 -P in the permeate water was nearly zero, indicating the complete rejection of PO4 -3 -P by the MD membrane. Due to membrane biofouling and scaling, wetting was observed for different durations at different temperatures. This study revealed that the An-FOMBR and An-MDBR combining with WFMF has a potential in exhibiting a continuous long-term operation and hence can serve as a sustainable solution for treating high strength textile wastewater. To avoid salinity built up in the bioreactors, study using salt absorbing microbial consortia (halophilic microbes) instead of using MF system is recommended. Also, study to use real textile wastewater through semi-pilot-scale An-FOMBR and An-MDBR combining with WFMF is highly recommended to achieve promising results and monetary value budgeting/costing for full scale-plant.