The performance and operational stability of the three pilot-scale SGBR for the treatment of industrial wastewater were investigated in this study. High organic removal efficiencies (over 94% of COD removal) were obtained from the two pilot-scale SGBR (R1 and R2) for the treatment of slaughterhouse wastewater. During the operation of reactors, the solid retention times over 240 and 150 days for the R1 and R2, respectively were obtained. The pilot-scale SGBR was also successfully employed for treating dairy processing wastewater under psychrophilic conditions. COD, BOD, and TSS removal rates obtained were 93, 96, and 90%, respectively, even at low temperatures of 11°C. The SGBR achieved average COD, BOD, and TSS removal efficiencies higher than 91% even at high loading rates up to 7.31 kg COD/m3/d with an HRT of 9 h. The of three pilot-scale SGBR were operating in a stable condition since pH values were in the optimal range and VFA/alkalinity ratios were fairly low throughout the experimental period. The average methane yield of 0.26 L CH4/g CODremoved was possibly affected by a high fraction of particulate COD and operation at low temperatures. In addition to the conversions of soluble COD into methane, particulate organic matter was physically retained by adsorption to granular sludge and the entrapment of coarse suspended solids in the sludge bed. Increased headloss through the granular bed due to the accumulated excess biomass and the retained solids were controlled by periodic backwashing.

A proper backwash rate is necessary to ensure effective removal of dispersed fine sludge and excessive suspended solids. Assuming that the average granule size and density in this study are in the range of 0.8-1.6 mm and 1000-1060 kg/m3, respectively, the minimum backwash rates varied from 0.02 to 4.34 m/h depending on the size and density of the granules. The proper backwash velocity ranged from 0.11 to 11.33 m/h based on the assumption that the bed porosity increased up to 0.4 and 50% expansion was selected as the optimum value. Therefore, backwash at a flow rate of 10-15 gpm (3.91-5.87 m/h) was applied to the pilot-scale SGBR (cross-sectional area: 6.25 ft2) treating dairy wastewater in Tulare, CA.

Performance of the lab-scale RRP biofilter was compared to a conventional gravel system and a peat biofilter system for treatment of septic tank effluent. During the study, the RRP biofilter provided similar or better performance than other systems in terms of organic removal and hydraulic capacity. After the start-up period, RRP biofilter achieved removal efficiencies for BOD5, TSS, ammonia nitrogen of 96, 93, and 90%, respectively, over the range of hydraulic loading rates of 1.4 to 5.0 gpd/ft2. On the other hand, the peat biofilter failed hydraulically and the gravel system showed high TSS concentrations in the effluent. RRP provided high surface area and sufficient time for biological treatment. In addition, RRP provided a non-toxic media for biofilm attachment in biofilter. RRP was observed to provide ammonia adsorption capacity. The results showed that RRP has the potential to be used as substitutes for natural aggregate such as gravel in septic system drainfields. The RRP biofilter can be used as alternative septic systems for the sites where an existing septic system has failed or site conditions, such as high groundwater table or small lot size, are not suitable for the installation of conventional septic systems.