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Three pilot-scale, horizontal-flow biofilm reactors (HFBRs 1-3) were used to treat methane (CH 4 )-contaminated air to assess the potential of this technology to manage emissions from agricultural activities, waste and wastewater treatment facilities, and landfills. The study was conducted over two phases (Phase 1, lasting 90 days and Phase 2, lasting 45 days). The reactors were operated at 10 C (typical of ambient air and wastewater temperatures in northern Europe), and were simultaneously dosed with CH 4 -contaminated air and a synthetic wastewater (SWW). The influent loading rates to the reactors were 8.6 g CH 4 /m 3 /hr (4.3 g CH 4 /m 2 TPSA/hr; where TPSA is top plan surface area). Despite the low operating temperatures, an overall average removal of 4.63 g CH 4 /m 3 /day was observed during Phase 2. The maximum removal efficiency (RE) for the trial was 88%. Potential (maximum) rates of methane oxidation were measured and indicated that biofilm samples taken from various regions in the HFBRs had mostly equal CH 4 removal potential. In situ activity rates were dependent on which part of the reactor samples were obtained. The results indicate the potential of the HFBR, a simple and robust technology, to biologically treat CH 4 emissions. Implications:The results of this study indicate that the HFBR technology could be effectively applied to the reduction of greenhouse gas emissions from wastewater treatment plants and agricultural facilities at lower temperatures common to northern Europe. This could reduce the carbon footprint of waste treatment and agricultural livestock facilities. Activity tests indicate that methanotrophic communities can be supported at these temperatures. Furthermore, these data can lead to improved reactor design and optimization by allowing conditions to be engineered to allow for improved removal rates, particularly at lower temperatures. The technology is simple to construct and operate, and with some optimization of the liquid phase to improve mass transfer, the HFBR represents a viable, cost-effective solution for these emissions.

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A novel horizontal flow biofilm reactor (HFBR) has been adapted and tested for its efficiency in treating hydrogen sulphide (H(2)S) and methane (CH(4)) gas. Six pilot-scale HFBR reactors were commissioned, three each treating CH(4) and H(2)S respectively. The reactors were operated at 10 °C, often typical of ambient temperatures in Ireland, and were simultaneously dosed with an air mixture containing the gas in question and with synthetic wastewater (SWW). Three reactors (HFBR 1, 2 and 3), treating an air mixture containing CH(4), were operated over three phases (Phases 1-3) lasting 180 days in total. During each phase the air mixture flow rate (AFR) and the plastic media top plan surface area (TPSA) loading rate to HFBR 1, 2 and 3 were 1.2 m(3)/m(3)/h and 0.6 m(3)/m(2) TPSA/h respectively. In Phase 1 the reactors were operated in triplicate and were loaded with 8.6 g CH(4)/m(3) reactor/h (4.3 g CH(4)/m(2) TPSA/h) and a synthetic wastewater (SWW) similar to domestic sewage at 10 °C. During Phase 2 (reactors also operated in triplicate) the effect of temperature on the reactor performance was examined. During Phase 3 the reactors were operated independently in order to examine the effects of omitting organic carbon and adding additional nitrogen in the form of nitrate-nitrogen (NO(3)-N), rather than ammonium-nitrogen (NH(4)-N). During Phase 3, CH(4) removal efficiencies (RE) of up to 92.8% were achieved at an empty bed retention time (EBRT) of 50 min, equating to a maximum removal of 8.0 g CH(4)/m(3) reactor/h. Three additional reactors (HFBR 4, 5 and 6) were used to treat an air mixture containing H(2)S and were loaded at an AFR of 15 m(3)/m(3) reactor/h (7.5 m(3)/m(2) TPSA/h) with an average H(2)S loading rate of 3.34 g H(2)S/m(3) reactor/h (1.67 g H(2)S/m(2) TPSA/h). After 50 days of operation, the RE reached 100% for all three reactors at an EBRT of 4 min. In each reactor, profile samples of biofilm, air and liquid were taken periodically from various regions of the HFBR. These allowed detailed description of removal processes and optimisation of the reactors by detailing changes in air, liquid and biofilm composition as air moved through the reactor.

A four-month experiment was conducted to evaluate the toxicity of a sewage effluent using both single-species and whole ecosystem tests. Fresh effluent from the East Greenwich, Rhode Island, sewage treatment plant was added daily to six experimental ecosystems (mesocosms). Sewage effluent additions were made at 0.1, 1.0, and 10% of the daily seawater input (960 L/day) from Narragansett Bay. Reagent grade, inorganic nutrients were added to the control, 0.1% and 1.0% effluent treatments to normalize nutrient loadings in all treatments. The Arbacia punctulata sea urchin sperm cell test was conducted on effluent and mesocosm samples. In the mesocosms, measurements of responses at the population, community, and ecosystem levels of biological organization were made. The single-species toxicity test indicated the mean EC50 of the sewage effluent was 1.1%. Toxicity decayed rapidly over time, and was unrelated to carbon, nutrient, residual chlorine, or metal concentrations. Toxicity in the mesocosms was variable due to short-term (4 to 5 h), incomplete mixing of the effluent. There was no evidence for a buildup of toxicity in the mesocosms. Mesocosm effluent additions decreased phytoplankton standing stock and produced an imbalance between total system production and respiration leading to hypoxia. At the 10% effluent loading, net system production was negative. Results indicated both single-species and mesocosm approaches were useful to assess toxicity. The single-species test was best utilized to characterize the magnitude and persistence of toxicity, and the mesocosm experiments were best employed to identify sensitive communities and processes.