A pilot-scale (1,000 L) continuous flow microbial electrolysis cell was constructed and tested for current generation and COD removal with winery wastewater. The reactor contained 144 electrode pairs in 24 modules. Enrichment of an exoelectrogenic biofilm required ~60 days, which is longer than typically needed for laboratory reactors. Current generation was enhanced by ensuring adequate organic volatile fatty acid content (VFA/SCOD ≥ 0.5) and by raising the wastewater temperature (31 ± 1°C). Once enriched, SCOD removal (62 ± 20%) was consistent at a hydraulic retention time of 1 day (applied voltage of 0.9 V). Current generation reached a maximum of 7.4 A/m(3) by the planned end of the test (after 100 days). Gas production reached a maximum of 0.19 ± 0.04 L/L/day, although most of the product gas was converted to methane (86 ± 6%). In order to increase hydrogen recovery in future tests, better methods will be needed to isolate hydrogen gas produced at the cathode. These results show that inoculation and enrichment procedures are critical to the initial success of larger-scale systems. Acetate amendments, warmer temperatures, and pH control during startup were found to be critical for proper enrichment of exoelectrogenic biofilms and improved reactor performance.

A 2-year pilot study was conducted by the City of Malmo, Sweden, to determine the maximum capacity of existing trickling filters when converted from carbonaceous duty to nitrification duty. Operating variables examined included a comparison of alternating two-stage to single-stageoperation, flushing intensity, and predator control techniques. Distributor speed control had only a small effecton nitrification efficiency, and motorized distributors are not required in this application. Twostage operation in an alternating mode provided for higher nitrification rates and lower effluent ammonia values than in single-stage operation. A nitrification model was used to analyze reaction rate data. The analysis showed that alternating two-stage operation mitigated the suppressing effect of influent suspended solids, resulting in enhanced nitrification rates. The filter macrofauna were dominated by worms rather than filter flies, so that regular filter flooding did not enhance nitrification rates.Waler Environ. Res.. 67, I11I (1995).

The existing theories incorporated to state‐of‐the‐art, activated‐sludge‐consensus models indicate that the removal of particulate substrate from the liquid in the activated‐sludge process is a two‐step process: instantaneous enmeshment of particles and hydrolysis followed by oxidation. However, experimental observations indicate that the removal of particles is not instantaneous and needs a more accurate description. This removal process can actually be described as a three‐step process: flocculation, hydrolysis, and oxidation. The principal objective of this research was to observe and model the kinetics of the removal of suspended particles and colloidal particles. A first‐order, particulate‐removal expression, based on flocculation, accurately described the removal rates for supernatant suspended solids and colloidal chemical oxygen demand (COD). The rate of reaction for removal of colloidal COD was slow and comparable to that for soluble organic matter.

The success of gravity separation of activated sludge from a treated effluent depends on the flocculent nature of the mixed liquor entering the secondary clarifier. Despite its importance to the overall effectiveness of the activated sludge process, flocculation phenomena are not routinely considered in the design and operation of the process. Further optimization of the activated sludge process to meet higher performance demands requires that the competing reactions of floc aggregation and breakup be maximized and minimized, respectively. Accordingly, the goal of this study was to develop an improved understanding of activated sludge flocculation.
A theoretically based and easily performed batch flocculation procedure was developed. The procedure enabled the quantification of the flocculation characteristics of activated sludges. The procedure was field applied, testing 30 activated sludges obtained at 21 full‐scale facilities. Results obtained during the field study indicated that the equilibrium concentration of supernatant suspended solids following batch flocculation and settling is comparable for a wide variety of activated sludges regardless of the initial aggregative state of the mixed liquors or the aeration device employed. The results indicated that flocculation of activated sludge cannot be used to reduce supernatant suspended solids below a certain limit. Moreover, the results indicated that attainment of equilibrium is rapid; the activated sludge flocculation reaction in batch reactors was 99% complete within 10 minutes for all but six of the activated sludges studied. Field‐determined estimates of activated sludge flocculation characteristics can be used to predict the performance of flocculators placed either upstream of or in secondary clarifiers. These estimates also can be used to determine the impact of altering process variables on flocculation, thereby affording a procedure for optimizing an activated sludge's flocculation potential.

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