Life-Cycle Energy Use and Greenhouse Gas Emissions of a Building-Scale Wastewater Treatment and Nonpotable Reuse System.

Treatment and water reuse in decentralized systems is envisioned to play a greater role in our future urban water infrastructure due to growing populations and uncertainty in quality and quantity of traditional water resources. In this study, we utilized life-cycle assessment (LCA) to analyze the energy consumption and greenhouse gas (GHG) emissions of an operating Living Machine (LM) wetland treatment system that recycles wastewater in an office building. The study also assessed the performance of the local utility's centralized wastewater treatment plant, which was found to be significantly more efficient than the LM (79% less energy, 98% less GHG emissions per volume treated). To create a functionally equivalent comparison, the study developed a hypothetical scenario in which the same LM design flow is recycled via centralized infrastructure. This comparison revealed that the current LM has energy consumption advantages (8% less), and a theoretically improved LM design could have GHG advantages (24% less) over the centralized reuse system. The methodology in this study can be applied to other case studies and scenarios to identify conditions under which decentralized water reuse can lower GHG emissions and energy use compared to centralized water reuse when selecting alternative approaches to meet growing water demands.

A full-scale study of mixing and foaming in egg-shaped anaerobic digesters.

Seasonal foaming in full-scale egg-shaped digesters (ESD) at the Oceanside Water Pollution Control Plant was investigated over a two-year period. The causes and contributors of anaerobic digestion (AD) foaming, namely, Gordonia amarae filaments and mixing effects were evaluated in these ESDs. The seasonal presence of high levels of G. amarae as a primary cause and excessive induced mixing as an important contributor of AD foaming has been established. The induced mixing frequency in the ESDs was gradually reduced and eventually shut off in a series of controlled experimental phases. Total solids and temperature profiles indicated that reducing mixing frequency did not significantly impact digester performance or disrupt the homogeneity of digester contents, although it did reduce the occurrence of foam in the digesters. Excessive induced mixing, a contributor to foaming, increased foam events at G. amarae thresholds above 10(6)intersections/mg VSS in the mixed liquor.

Control of partial nitritation of centrate in a sequencing batch reactor.

This research identified suitable conditions for long-term inhibition of nitrite-oxidizer bacteria (NOB) in a sequencing batch reactor for the treatment of centrate by over-nitrite pathways. The NOB were inhibited by free ammonia concentrations greater than 20 mg NH3-N/L combined with a dissolved oxygen concentration less than 0.3 mg O2/L and a temperature of 30 degrees C. The experiments were performed in a laboratory-scale 2.5-L reactor fed with synthetic and actual centrate from a full-scale wastewater treatment plant (800 to 1500 mg NH4+ -N/L). The influence of influent-alkalinity-to-ammonium ratio (AAR) on the effluent-nitrite-to-ammonium ratio (NAR) also was investigated. The control of the effluent NAR was possible by adjusting the influent AAR when NOB inhibition was maintained and when total alkalinity depletion took place before the end of the cycle. The maximum nitritation rate of 860 mg NO2- -N oxidized/L x d was obtained when the influent NH4+ -N concentration was 800 mg NH4+ -N/L and the hydraulic retention time was 1.7 days.