Utilization of a hybrid sequencing batch reactor (HSBR) as a decentralized system of domestic wastewater treatment.

This paper presents the experiments carried out in a hybrid sequencing batch reactor (HSBR), used for biological treatment of sewage. The HSBR was built in a cylindrical shape and made of stainless steel, with a volume of 1.42 m3. Besides the biomass in suspension, the reactor also carried fixed biomass (hybrid process), adhered in the support material. This consisted of a nylon net disposed in a grille for biofilm biomass adhesion. The reactor worked fully automated in operational cycles of maximum 8 hours each, presenting the following phases: filling, anoxic, aerobic, settle and draw of treated effluent, with 3 fillings per cycle. Increasing organic loads (0.14 to 0.51 kg TCOD/m3 day) and ammonium loads (0.002 to 0.006 kg NH4-N/m3.day) were tested. We monitored the reactor's performance by measuring the liquid phase (COD, pH, temperature, DO, nitrogen and phosphorus) during the cycles and by measuring the sludge through respirometric tests. The results obtained demonstrated TCOD removal efficiency between 73 and 96%, and ammonium removal efficiency between 50 and 99%. At the end of the cycles, the effluent presented ammonium concentration <20 mg/L, meeting the Brazilian environmental legislation standards (CONAMA 357/2005) regarding discharges into the water bodies. Respirometric tests showed biomass dependency on FCOD concentrations. Results have demonstrated the potential of this type of reactor for decentralized treatment of domestic wastewater.

Reduction of odors from a facultative pond using two different operating practices.

This paper presents the results of a proposed intervention to deal with the odor problems of a sewage treatment works (STW), which is located near a populated area. The STW consists of a facultative pond. Since this pond functions under close to anaerobic conditions, unpleasant odors are emitted. In this respect, two possible ways to deodorize the pond were evaluated. Firstly, the recirculation of effluent using 1/6 of the flow stream followed by aeration of the pond with a reduced power aerator. In order to study the efficiencies of the deodorization methodologies chemical analyses of the gases NH3 and H2S, olfactometric analyses and evaluation of the environmental perception of the population in relation to the odors originating from the STW, were carried out for each experimental situation. The results showed a significant reduction in odors when aeration with reduced power equipment was utilized in combination with recirculation of effluent in the pond. Reductions in emissions of H2S from 0.1345 mg/m3 to 0.0083 mg/m3 and of NH3 from 0.021 mg/m3 to 0.0073 mg/m3 were obtained. To analyze the behavior of the pond, its planktonic community was investigated, with a difference in species for the situations with and without odor being observed.

Influence of load distribution and recycle rate in step-fed facultative ponds.

This study presents the results of research on a wastewater treatment system with four identical facultative ponds in series with step-feeding and recirculation (SFFPR). Four modes of distribution of the influent were studied, which were (in percentages of the inflow per pond): C1 = 25/25/25/25; C2 = 50/20/20/10; C3 = 50/50/0/0; C4 = 100/0/0/0. The organic loading applied to the four ponds overall was around 200 kg BOD5/ha.d. The distribution C4 = 100/0/0/0 was selected for studying the recycle rate. Three recycling rates were studied: 0.5Q, 1Q and 2Q. COD and BOD5 removal efficiencies were high whatever the step-feed distribution. For the distribution C1 and C2, the four ponds were homogeneous. The equal distribution of organic loading rate in C2 distribution was most beneficial for algal growth. For piston pattern distributions (C3 and C4), the ponds receiving the highest loading showed a bacterial biomass higher than that of the primary production. Increasing the recirculation rate seemed to lead towards homogenisation of the ponds, while a decrease appeared to lead to their individualisation and increased their productivity. The SFFPR constitutes a stage of the treatment process which can replace the facultative stage; it produces a high effluent quality and decreases land area requirements.