Capillary microbioreactors for VOC vapor treatment: Impacts of operating conditions.

Micro-capillary bioreactors (1 mm ID, 10 cm long) were investigated for the biodegradation of toluene vapors as a model volatile organic compound (VOC). The intended application is the removal of VOCs from indoor air, when such microbioreactor is coupled with a microconcentrator that intermittently delivers high concentrations of VOCs to the bioreactor for effective treatment. The effects of key operating conditions were investigated. Specifically, gas film and liquid film mass transfer coefficients were determined for different gas and liquid velocities. Both mass transfer coefficients increased with gas or liquid velocity, respectively, and the overall gas-liquid mass transfer was dominated by the liquid-side resistance. Experiments with the microbioreactors focused on the effects of gas velocity, liquid velocity and mineral medium renewal rate on the treatment of toluene vapors at different inlet concentrations. The best performance in terms of toluene removal and mineralization to CO2 was obtained when the gas and liquid velocity ratio was close to one and achieving Taylor or slug flow pattern. Sustained treatment over extended periods of time with toluene elimination capacities ranging from 4000 to over 9000 g m-3 h-1 were obtained, which is orders of magnitude greater than conventional biofilters and biotrickling filters. Biological limitations generally played a more important role than mass transfer limitation. Continuous mineral medium supply at a high rate (10 h liquid retention time) enabled pH control and provided ample nutrient supply and therefore resulted in better toluene elimination and mineralization. Overall, these studies helped select the most suitable conditions for high performance and sustained operation.

Nutrient removal from human fecal sludge digestate in full-scale biological filters.

There is a great need for simple methods for digestate management for potential household sanitation systems based on anaerobic digestion of minimally diluted fecal waste in countries that lack safe sanitation. Herein, a full-scale three-stage filter for nitrogen and phosphorus removal from anaerobic digester effluent was implemented in Madagascar. It included a trickling filter with crushed charcoal (for aerobic nitrification), a submerged anaerobic filter with bamboo chips (for denitrification), and a submerged filter with scrap iron (for phosphorus removal). All filter materials were sourced locally. Three parallel replicate systems were operated in two sequential 8-week phases for a total of 16 continuous weeks. Though the influent feed was not as expected, with much of nitrogen in the feed coming in as organic N and not as NH3-N, the filters still removed 38-49% of total incoming nitrogen. The filters achieved high rates of nitrogen transformation along with removing solids (73-82% turbidity removal), chemical oxygen demand (67-75% removal), and phosphorus (31-50% removal). Overall, the reaction rates from this full-scale study were in line with previous lab-scale investigations with scaled-down systems, supporting their application in real-world scenarios. Based on this study, simple effluent filters can support nutrient removal for small-scale and onsite fecal sludge treatment systems.

Resources recovery from high-strength human waste anaerobic digestate using simple nitrification and denitrification filters.

Simple trickling nitrification filters and submerged denitrification filters were developed to provide post-treatment to high-strength human waste anaerobic digestate with the aims to (i) effectively recover nutrients in a useful form as a fertilizer and to (ii) treat digestate such that it could be reused as flush water in water scarce regions. The tested filter media (biochar, granular activated carbon, rice and coconut husks, bamboo chips, sunflower seeds, and zeolite) are low cost and sustainable materials and can be locally sourced where on-site sanitation facilities are in high demand. Experimental data from laboratory operation with digestate from anaerobic digestion of dog feces and human urine revealed that the filters achieved a combined removal of chemical oxygen demand (COD), total nitrogen (TN), and phosphorus (PO4-P) up to 84%, 69%, and 89%, respectively. Post-treatment filters have also demonstrated successful recovery of vital nutrients by precipitating ammonium magnesium phosphate hydrate, a documented valuable slow-release solid fertilizer. These filters have a great potential for advancing access to improved sanitation while simultaneously increasing capacity for small-scale economic agricultural development in geographic regions lacking improved sanitation.

Miniaturized Biotrickling Filters and Capillary Microbioreactors for Process Intensification of VOC Treatment with Intended Application to Indoor Air.

Typical biofilters and biotrickling filters used for volatile organic compounds (VOCs) control have treatment rates limited to 30-200 g m-3 h-1, mostly because they are exposed to dilute VOC streams, have moderate biomass density and activity, and moderate mass transfer coefficients. For these reasons and the concern over releasing bioaerosols and humidity, traditional biofilters and biotrickling filters are not ideal for the treatment of indoor air. Here we report on the development and evaluation of microbioreactors for the intensive treatment of VOCs that could be used for indoor air quality control, when coupled with a VOC microconcentrator (developed separately). The microconcentrator will function to adsorb VOCs from indoor air and release them to the microbioreactor at a higher concentration. The miniaturized bioreactors, with maximized surface area-to-volume ratios, allow for increased mixing and mass transfer of pollutants to the biofilm, resulting in a greater degradation rate of the VOCs. Three different microbioreactors were designed, constructed and their performance for removing vapors of toluene and methanol was assessed. Results showed that they were able to achieve maximum elimination capacities (ECs) for methanol around 1000 g m-3 h-1, 780 g m-3 h-1, and 12 600 g m-3 h-1 for the glass beads packed bed, polyurethane (PU) foam biotrickling filters and capillary microbioreactor, respectively, and around 120 g m-3 h-1, 250 g m-3 h-1 and 3050 g m-3 h-1, respectively, when treating toluene vapors. These values, especially for the capillary microbioreactor, are 40-80 times greater than the rates generally obtained in conventional biofilters and biotrickling filters. The interphase mass transfer coefficient (KLa) was determined. The capillary microbioreactor had values 13-17 times greater than the other two bioreactors, suggesting that improved mass transfer could have contributed to the very high performance observed in the capillary microbioreactor. The results demonstrate that microbioreactors are promising novel technologies for controlling small amounts of organic pollutants.

Performance evaluation of a full-scale innovative swine waste-to-energy system.

Intensive monitoring was carried out to evaluate the performance of a full-scale innovative swine waste-to-energy system at a commercial swine farm with 8640 heads of swine. Detailed mass balances over each unit of the system showed that the system, which includes a 7600m(3) anaerobic digester, a 65-kW microturbine, and a 4200m(3) aeration basin, was able to remove up to 92% of the chemical oxygen demand (COD), 99% of the biological oxygen demand (BOD), 77% of the total nitrogen (TN), and 82% of the total phosphorous (TP) discharged into the system as fresh pig waste. The overall biogas yield based on the COD input was 64% of the maximum theoretical, a value that indicates that even greater environmental benefits could be obtained with process optimization. Overall, the characterization of the materials fluxes in the system provides a greater understanding of the fate of organics and nutrients in large scale animal waste management systems.

Water Availability for Shale Gas Development in Sichuan Basin, China.

Unconventional shale gas development holds promise for reducing the predominant consumption of coal and increasing the utilization of natural gas in China. While China possesses some of the most abundant technically recoverable shale gas resources in the world, water availability could still be a limiting factor for hydraulic fracturing operations, in addition to geological, infrastructural, and technological barriers. Here, we project the baseline water availability for the next 15 years in Sichuan Basin, one of the most promising shale gas basins in China. Our projection shows that continued water demand for the domestic sector in Sichuan Basin could result in high to extremely high water stress in certain areas. By simulating shale gas development and using information from current water use for hydraulic fracturing in Sichuan Basin (20,000-30,000 m(3) per well), we project that during the next decade water use for shale gas development could reach 20-30 million m(3)/year, when shale gas well development is projected to be most active. While this volume is negligible relative to the projected overall domestic water use of ∼36 billion m(3)/year, we posit that intensification of hydraulic fracturing and water use might compete with other water utilization in local water-stress areas in Sichuan Basin.

Natural Gas Residual Fluids: Sources, Endpoints, and Organic Chemical Composition after Centralized Waste Treatment in Pennsylvania.

Volumes of natural gas extraction-derived wastewaters have increased sharply over the past decade, but the ultimate fate of those waste streams is poorly characterized. Here, we sought to (a) quantify natural gas residual fluid sources and endpoints to bound the scope of potential waste stream impacts and (b) describe the organic pollutants discharged to surface waters following treatment, a route of likely ecological exposure. Our findings indicate that centralized waste treatment facilities (CWTF) received 9.5% (8.5 × 10(8) L) of natural gas residual fluids in 2013, with some facilities discharging all effluent to surface waters. In dry months, discharged water volumes were on the order of the receiving body flows for some plants, indicating that surface waters can become waste-dominated in summer. As disclosed organic compounds used in high volume hydraulic fracturing (HVHF) vary greatly in physicochemical properties, we deployed a suite of analytical techniques to characterize CWTF effluents, covering 90.5% of disclosed compounds. Results revealed that, of nearly 1000 disclosed organic compounds used in HVHF, only petroleum distillates and alcohol polyethoxylates were present. Few analytes targeted by regulatory agencies (e.g., benzene or toluene) were observed, highlighting the need for expanded and improved monitoring efforts at CWTFs.