Hours Of Hydraulic Retention Time Research Articles

Performance Upgrading Evaluation of the Anaerobic Baffled Reactor by Integrating Aerobic Media Filter for Municipal Wastewater Treatment

Background & Aims of the Study: Anaerobic baffled reactor (ABR) is one of the low-cost wastewater treatment systems; however, it has some limitations, such as insufficient standard nutrient outflow. Accordingly, it should be studied and developed. This research aims to determine the efficiency of a five-sectional reactor pilot and to upgrade it with an integrated aerated media filter in the reactor (integrated reactor) for municipal wastewater treatment. Materials and Methods: This study was performed on a laboratory scale with field conditions in the Khoy City wastewater treatment plant. The ABR reactor operated for 270 days with a hydraulic retention time (HRT) of 48, 36, 24, and 18 hours, respectively. The Integrated anaerobic baffled reactor (IABR) was operated for 35 days with 24 hours of HRT, i.e., aeration time of 5 hours. The reactors were fed in line from the inflowing wastewater to the treatment plant. A 24-hour combined sampling was performed 224 times from the inflow and outflow of the system, and volatile suspended solids, total kjeldahl nitrogen (TKN), total phosphorus (TP), biochemical oxygen demand (BOD), chemical oxygen demand (COD), and Total Suspended Solids (TSS) parameters were measured and compared with the effluent disposal standard. Results: The launch of ABR lasted 105 days, and its helpful operation lasted 200 days. In 18 to 48 hours, the reactor removed 79% to 91% of COD, 9% to 20% of TKN, 19% to 30% of phosphorus, and 89% to 94% of TSS. The IABR reached the effluent disposal standard in terms of TSS, BOD, COD, and phosphorus under 24 hours HRT, i.e., aeration time of 5 hours, and increased the COD removal efficiency by 6% compared to ABR under 24 hours HRT and the same conditions. Conclusion: By integrating the final aerobic media filter in ABR while reducing the required HRT by 50%, its efficiency in achieving the effluent disposal standards increased compared to ABR. Therefore, this system can be used to treat municipal wastewater.

Zeolitas nativas en el tratamiento de agua residual doméstica

En esta investigación zeolitas de río y de cerro fueron evaluadas para ver su potencial en el tratamiento de aguas residuales. En primer lugar, se diseñó y construyó un sistema experimental de tres biorreactores de lecho fijo de flujo ascendente (BLFFA) con una altura de 1.5 metros y diámetro de cuatro pulgadas, seguidamente se evaluó el potencial de las zeolitas nativas y una testigo comercial en el tratamiento de aguas residuales. Se arrancaron los BLFFA con un diseño factorial 3 x 3, operando con zeolita de río, zeolita de cerro y zeolita comercial (control), todas con partículas de ¼ de pulgada, utilizando tres diferentes alturas de lecho (0.75, 0.90 y 1.10 m) y tres tiempos de retención hidráulica (6, 12 y 24 horas). Se evaluaron las variables de respuesta mediante un análisis de varianza multifactorial y para discriminar entre las medias se empleó el método de diferencia mínima significativa (LSD) de Fisher (p < 0.05, 95 % de confianza). La zeolita de cerró presentó (promedio, N = 10) las mejores características fisicoquímicas con densidad real y aparente de 2700 y 1470 kg/m3 respectivamente, peso específico de 2240 kg/m3, porosidad de 62 %, absorción de 15.20 %, solubilidad en ácido clorhídrico de 29.96 %, pH de 7.4 y conductividad eléctrica de 70 mS/cm. Al agua residual con las que se desarrollaron los tratamientos se le aplicó previo al experimento un tratamiento primario (rejilla, desarenador, desnatador y fosa séptica) y presentó valores (promedio, N = 9) de temperatura de 25.26 °C, pH de 8.63, sólidos disueltos totales con 950.50 mg/L, color de 1305.10 UC, turbiedad 96.37 UNT y demanda química de oxígeno de 373 mg/L. De las zeolitas evaluadas (N = 81) en el BLFFA, la que presentó el mejor tratamiento fue la zeolita de cerro operando con una altura de lecho de 0.9 m y con 24 horas de tiempo de retención hidráulica; obtuvo las mejores eficiencias de remoción con 71.42 % en sólidos disueltos totales, 84.34 % para turbiedad, 96.33 % para color y 97.28 % para la demanda química de oxígeno. La altura óptima en los BLFFA fue 0.9 m, factor importante de evaluar, ya que a mayor altura se aumentan los costos y las eficiencias no son relevantes para justificar la inversión y a menor altura cae el rendimiento en calidad del agua tratada. En conclusión, las zeolitas nativas cuentan con propiedades idóneas para ser utilizadas en el tratamiento de agua residual doméstica y podemos recomendar la implementación de los BLFFA en el tratamiento secundario de efluentes domésticos en sistemas descentralizados del sureste de México como una alternativa viable en el tratamiento de sus aguas residuales domésticas.

Upgradation of conventional MBBR into Aerobic/Anoxic/Aerobic configuration: A case study of carbon and nitrogen removal based sewage treatment plant

The thrust of this study was to assess the upgradation of an existing 3.5 million liters per day (MLD) full-scale conventional MBBR-based sewage treatment plant (STP) into Aerobic/Anoxic/Aerobic configuration. Initially, the plant was designed and constructed for achieving BOD and TSS to <30 mg/L and <50 mg/L, respectively. Recently, due to the advent of stringent effluent standards for BOD (Biological Oxygen Demand), TSS (Total Suspended Solids), and TN (Total Nitrogen) to <10 mg/L, with a strong emphasis on non-potable re-use of treated effluent, the existing system needed intensive upgradation. The upgraded STP was modified from two hours to five hours of hydraulic retention time (HRT). The upgraded plant was examined by removing organic carbon and nitrogen from municipal wastewater through both partial nitrification-denitrification (PND) by aerobic and anoxic reactors and simultaneous nitrification and denitrification (SND) process by PVA (Poly Vinyl Alcohol) gel aerobic reactor. After ten months of operation and monitoring, the plant has reached its upgraded effluent discharge standard. It was found that average BOD, COD, TSS, TN, and TP (Total Phosphorus) concentrations were 8 mg/L, 25 mg/L, 12 mg/L, 9 mg/L and 5 mg/L respectively, with 91 %, 90 %, 93 %, 84 %, and 64 %, removal efficiency. It was observed that PVA-gel beads are not only efficient for carbon removal (BOD & COD) but also achieve high SND rates.

Sustainable treatment of domestic wastewater through microalgae

The present work evaluated the optimum concentration of microalgal cells for domestic wastewater treatment in terms of removal in nutrients and physicochemical parameters. In the study, three different concentrations (20, 30, and 40%) of microalgae was considered at 8 hours and 24 hours of Hydraulic Retention time (HRT). Among the different microalgal concentrations studied 30% microalgae concentration gave maximum removal at both the HRTs. The maximum removal efficiency of phosphate, ammonia and COD for the non-filtered sample was 87.67, 96.88, and 80.39%, respectively, for filtered sample it was about 91.32, 100, and 83.64%, respectively at 8 hours HRT. However, at 24 hours HRT maximum removal efficiency observed was 97.92, 92.22, and 93.47% for ammonia, COD and phosphate respectively in case of non-filtered sample whereas in filtered samples maximum removal efficiency was 100, 94.44, and 95.51% for ammonia, COD and phosphate respectively. From the study, it was found that microalgae can effectively remove nutrients and organic contents to desirable limits even at a low HRT of 8 hours. At the urban sector, if microalgae are incorporated in a conventional wastewater treatment system will enhance the cost-effective efficiency by lowering the HRT and increasing the removal efficiency with footprints of sustainable treatment.

Treatment of surface water contaminated arsenite using continuous flow air-cathode electrocoagulation

Air-cathode Electrocoagulation (ACEC) is a new emerging technology that combines the concepts of electrocoagulation and fuel cell technology for treating water contaminated by pollutants without the addition of external energy. In this study, the ACEC reactor was used for the removal of Arsenite (As3+) contained in river water. The effects of the different anode materials and hydraulic retention time (HRT) to the performance of the reactor were investigated. The water containing 3,5 ppm of arsenite was used as a representation of river water contaminated by heavy metal. Three types of metal plates (magnesium, iron, and aluminum) were used as anode materials, while a wet-proof (30%) carbon cloth used as a cathode electrode. The reactor performance was evaluated by measuring the removal efficiency of arsenite, metal hydroxide concentration, current density, and maximum power density of the reactor. The result showed that the ACEC reactor with iron, aluminium, and magnesium anode were able to remove 99%, 17%, and 73% of arsenite respectively. In further experiments, the reactor was conducted in continuous mode with 4, 8, and 12 hours of HRT. The ACEC reactor with 12 hours HRT was able to remove arsenite up to 99% for 24 hours. This result indicated that ACEC process is a promising technology for the effective removal of arsenite from aqueous solution without additional energy.

Biofouling Formation and Bacterial Community Structure in Hybrid Moving Bed Biofilm Reactor-Membrane Bioreactors: Influence of Salinity Concentration

Two pilot-scale hybrid moving bed biofilm reactor-membrane bioreactors were operated in parallel for the treatment of salinity-amended urban wastewater under 6 hours of hydraulic retention time and 2500 mg L−1 total solids concentration. Two salinity conditions were tested: the constant salinity of 6.5 mS cm−1 electric conductivity (3.6 g L−1 NaCl) and the tidal-like variable salinity with maximum 6.5 mS cm−1 electric conductivity. An investigation was developed on the biofouling produced on the ultrafiltration membrane surface evaluating its bacterial community structure and its potential function in the fouling processes. The results showed that biofouling was clearly affected by salinity scenarios in terms of α-diversity and β-diversity and bacterial community structure, which confirms lower bacterial diversity under variable salinity conditions with Rhodanobacter and Dyella as dominant phylotypes. Microorganisms identified as bio-mineral formers belonged to genera Bacillus, Citrobacter, and Brevibacterium. These findings will be of help for the prevention and control of biofouling in saline wastewater treatment systems.

PENGHILANGAN AMONIAK DI DALAM AIR LIMBAH DOMESTIK DENGAN PROSES MOVING BED BIOFILM REACTOR (MBBR)

The treatment process of wastewater contains organic pollutant which used in Indonesia especially in Jakarta is generaly activated sludge process. The problem is its treated water quality which frequently does not yet fulfilled to effluent standard of wastewater. Some affecting factors are hydraulic retention time (HRT) too short, the fluctuation of wastewater flow rate, unfavorable function of aeration process and also which do not less important is operational mistake caused by insufficient knowledge of operator. To overcome the mentioned problems it is needed technological innovation to increase efficiency of wastewater treatment process especially activated sludge process. Moving Bed Biofilm Reactor (MBBR) technology is one of the effective alternative for treating wastewater containing organic pollutants. In principle, MBBR is a modification of the activated sludge process is enhanced by adding the media into the aeration tank.This paper describes the study of domestic waste water treatment using MBBR process which is filled with bioball plastic media which has specific surface 210 m2/m3 as much as 20 % of the volume of the aeration tank for attaching microorganism to increase efficiency and keep stability of process.Result of the study shows that within 12 hours, 8 hours, 6 hours and 4 hours of hydraulic retention time (HRT) in aeration tank and sludge circulation ratio 0f R = 1.0 Q, the removal efficiency of ammonia were 94.05 %, 93.42 %, 89 %, and 79.6 % respectively. In ammonia loading 0.106 – 0.302 kg/m3.day, the removal efficiency of ammonia were 95.54 – 83.01 %. The greater ammonia loading, removal efficiency of ammonia is getting smaller. Optimal residence time is 6 hours with ammonia removal efficiency reached 89 %, and the average concentration of ammonia in the effluent of 8.3 mg per litre. Keyword : Domestic wastewater, ammonia, bioball, MBBR.

Biodegradation of 2,4-dichlorophenol in Packed-Bed Biofilm Reactor: Effect of Hydraulic Retention Time, Biogenic Substrate, and Loading Rate.

The removal of 2,4-dichlorophenol (2,4-DCP) by a pure culture of Bacillus endophyticus strain immobilized on ceramic balls was studied in a packed bed biofilm reactor (PBBR). The biodegradation of 2,4-DCP was studied in fed-batch and continuous mode and the effect of different parameters such as hydraulic retention time (HRT), biogenetic substrate concentration, and loading rate on the removal of 2,4-DCP were evaluated. Field emission scanning electron microscope (FESEM) results established the biofilm formation on the ceramic beads. The maximum volumetric removal rate found to be 127.2 mg/L·d at loading rate of 172.8 mg/L·d with 73.6% degradation (12.5 hours of HRT, 90 mg/L of 2,4-DCP, 0.2 g/L of peptone). The bioreactor showed more than 98% removal of 2,4-DCP at loading rate of 115.2 mg/L·d at 12.5 hours of HRT and 0.2 g/L of peptone. Effect of peptone showed that lower peptone concentration increases the removal efficiency; however, some peptone is necessary to maintain the 2,4-DCP removal efficiency.

Heavy Metals Removal from Swine Wastewater Using Constructed Wetlands with Horizontal Sub-Surface Flow

The removal efficiency of Cu and Zn from swine wastewater was evaluated as effected by three variables: the hydraulic retention time (HRT) (24, 48, 72 and 96 hours), two different plant species (Typha domingensis Pers. and Eleocharis cellulosa) and two different sizes of filter media (5 and 15 mm) using a horizontal sub-surface flow constructed wetland. From the results, a significant difference was observed in the removal efficiency of Cu and Zn with respect to different hydraulic retention times. The best results were obtained in the HRT of 96 hours for Zn where 96% removal of Zn with Typha domingensis Pers. specie with gravel of 15 mm (experimental unit 6) was achieved. For Cu, at 72 hours of HRT, the efficiency was nearly 100% in five of the six study units (1, 2, 3, 5 and 6). In contrast, in experimental unit 4 with gravel of 15 mm and without plants, only 86% Cu removal was achieved.

Combination of photo-Fenton and biological SBBR processes for sulfamethoxazole remediation

A combined strategy of a photo-Fenton pretreatment followed by a Sequencing Batch Biofilm Reactor (SBBR) was evaluated for total C and N removal from a synthetic wastewater containing 200 mg L(-1) of the antibiotic Sulfamethoxazole (SMX). Photo-Fenton reaction was performed with two different H2O2 concentrations (300 and 400 mg L(-1)) and 10 mg L(-1) of Fe2+. The pre-treated effluents with the antibiotic intermediates as sole carbon source, together with a nutrients solution, were used as feed for the biological reactor. The SBBR was operated under aerobic conditions to mineralize the organic carbon and the hydraulic retention time (HRT) was optimized down to 8 hours. Then, an anoxic denitrification stage of 24 hours of HRT was added right after the aerobic stage of the same duration in order to remove the NO3(-) generated along the chemical-biological treatment. TOC, COD and SMX concentrations together with O2 uptake rate (OUR) profiles were monitored in purpose of assessing the performance of the system. NO3(-), NH4+ and total N concentrations were analyzed to find out the fate of N contained in the initial SMX molecule. A start up strategy resulted in the correct formation of a biofilm over the volcanic support. The total TOC removals achieved with the combination of the chemical and the biological processes were 75.7 and 87.7% for the low and the high H2O2 concentration pretreatments respectively. Practically all N present in the SMX solution was eliminated in the SBBR when the aerobic-anoxic strategy was used.

鉄酸化細菌を活用したスラリー型反応装置による電気メッキ排水からの金属分離回収

Wastewater from electroplating plants contains several metallic ions such as iron, nickel and zinc. In general, neutralization followed by sedimentation has been used for the treatment of electroplating wastewater. However, this process results in the production of large amounts of heavy metal sludge. The objective of this research is to achieve selective metal separation, metal recovery and reduction in sludge volume. We have examined the feasibility of a biological process using iron-oxidizing bacteria in the treatment of electroplating wastewater from steel works. It was proved that iron-oxidizing bacteria acclimated from activated sludge have the ability to oxidize ferrous ion (Fe2+) to ferric ion (Fe3+) in electroplating wastewater. A bioslurry reactor, which promotes both Fe2+ oxidation and Fe(OH)3 generation in the pH range from 3.0 to 4.0, showed an almost complete Fe2+ oxidization after 2 hours of hydraulic retention time. The produced Fe(OH)3 was recovered by sedimentation in the same pH range with almost no trace of nickel or zinc. Nickel and zinc hydroxides were easily recovered by sedimentation at pH 9.0.

Two-stage entrapped mixed microbial cell process for simultaneous removal of organics and nitrogen for rural domestic sewage application

A two-stage entrapped mixed microbial cell ((2S)EMMC) process which separates nitrification and denitrification phases by the installation of the anoxic and oxic EMMC reactors packed with EMMC carriers was operated with 6, 4, 3, and 2 hours of hydraulic retention time (HRT) using simulated domestic wastewater. The activated sludge was immobilized using cellulose acetate for the EMMC carriers. Similar soluble chemical oxygen demand (SCOD) removal efficiencies of 90-97% were observed for all HRTs (SCOD loading rate of 0.84-2.30 g/L/d) applied. In order to achieve more than 80% of TN removal efficiency, the HRT should be maintained higher than 4 hours (less than 0.24 g/L/d of TN loading rate). Denitrification was a rate-limiting step which controlled overall TN removal efficiency at TN loading rate of 0.15-0.31 g/L/d although nitrification efficiencies achieved 97-99%. The effluent TSS of less than 25 mg/L in the (2S)EMMC process was maintained at the SCOD loading rate of less than 1.23 g/L/d with back-washing intervals of 5 and 10 days in the anoxic and oxic EMMC reactors, respectively. The minimum HRT of 4 hours is required for high removal efficiencies of organics (average 95.6%) and nitrogen (average 80.5%) in the (2S)EMMC process with 3 times of recirculation ratio.

High-rate anaerobic hydrolysis and acidogenesis of sewage sludge in a modified upflow reactor

Continuous experiments were conducted to study the hydrolysis and acidogenesis of sewage sludge in an upflow reactor with an agitator and a gas-liquid-solid separator. Results of this study showed that 34-78% of volatile suspended solids (VSS) in sewage sludge was hydrolyzed at pH in the range 4.0-6.5, 35 degrees C and 4-24 hours of hydraulic retention time (HRT). About 31-65% of carbohydrate in sewage sludge, 20-45% of protein and 14-24% of lipid were acidified in this reactor. Hydrogen production was favored in lower pH and HRT, whereas methane production was encouraged at higher pH and HRT. Acetate, propionate, butyrate, and i-butyrate were the main aqueous acidogenic products. The distribution of these compounds in the effluent was more sensitive to pH, but was less sensitive to HRT. The maximu specific COD solubilization rate and specific volatile fatty acids production rate were 126 mg-COD/g-VSS x d and 102 mg-VFAIg-VSS x d, respectively. Compared with a CSTR, this modified upflow reactor was shown to be a more promising biosystem for the hydrolysis and acidogenesis of sewage sludge.

Effect of Copper Sulfate Addition on Nitrous-Oxide Emission in High Speed Denitrification Process Using Macro-Porous Cellulose Carrier

Nitrous oxide emission from the immobilized denitrification process was investigated under copper-added and copper-free conditions to realize high-speed denitrification with minimum nitrous oxide emission. Nitrous oxide emission was found to be smaller in culture using immobilized cells acclimatized under copper-added condition. Transient phenomena of nitrous oxide emission, nitrate reduction and nitrite accumulation were then investigated in repeated batch experiments by transferring immobilized cells acclimatized in copper-free conditions into copper-added medium. Nitrous oxide emission obviously decreased, and maximum nitrous oxide concentration of seventh batch culture was about 1/40000 of that of first batch culture. Nitrate reduction gradually decreased from second batch to fourth batch culture and it turned to increase from fifth batch culture to seventh batch culture. At seventh batch culture, nitrate reduction rate was restored up to 80% of the initial speed. This repeated batch experiment clarified that nitrous oxide emission was repressed by copper sulfate addition. The effect of pH and temperature on nitrous oxide emission were also investigated in a continuous denitrification experiment under copper added conditions. Nitrous oxide emission was increased by lowering pH and lowering temperature. At optimum operating condition (pH8.0, 30°C), nitrogen removal efficiency of 99.9%, nitrous-oxide concentration in the emitted gas of 3.1ppm(v/v) and conversion ratio to nitrous oxide of 0.000316% were obtained when 280mg-Nl−1 nitrate containing medium was treated at 6 hours of hydraulic retention time.

Degradation of phenol and p-cresol in reactors

The effects of hydraulic retention time (HRT) and phenol concentration on the degradation of phenol and p-cresol in wastewater were investigated in two respective UASB (upflow anaerobic sludge blanket) reactors with effluent recirculation at 37 °C for over 440 days. After acclimation, nearly all the phenol and p-cresol at moderate concentrations could be degraded without carbohydrate as a co-substrate. Treating a wastewater containing 800 mg/l of phenol and 300 mg/l of p-cresol at HRT ranging 2–12 hours, the first reactor consistently removed 95% of phenol, 65% of p-cresol and 85% of COD at 8–12 hours of HRT; the efficiency, however, decreased at lower HRT. Treating wastewater containing a constant p-cresol concentration of 400 mg/l at 24 hours of HRT, the second reactor was able to remove 75–80% of COD when the phenol was 1200 and 1500 mg/l; the removal efficiency decreased as phenol concentration further increased. High levels of residual phenol and p-cresol in the effluent suppressed the activity of biogranules. The suppression of bioactivity was not permanent. Biomass was able to regain its activity fully after lowering the phenolic concentrations in the wastewater.

Anoxic treatment of low-strength wastewater by immobilized sludge

Low levels of phenol and m-cresol were effectively removed from wastewater under anoxic condition using immobilized sludge. A 138-day experiment was conducted using wastewater containing NO3−-N (22.3 mg·1−1), phenol (10 mg·1−1) and m-cresol (5 mg·1−1) at 30°C using sucrose (50 mg·1−1) as co-substrate in an upflow reactor packed with polyvinyl alcohol (PVA) beads entrapped with anoxic sludge and powdered activated carbon (PAC). Throughout the experiment, phenol and m-cresol in the effluent were below the detectable level of 1.0 mg·1−1 even when HRT (hydraulic retention time) was as low as 0.55 hour. The effluent quality in general decreased with HRT. At 5.9 hours of HRT, the reactor effluent contained 5.9 mg·1−1 of COD (chemical oxygen demand) and 1.3 mg·1−1 of NO3−-N; but at 0.55 hour, they were, 17.3 and 5.7 mg·1−1, respectively. The effluent COD was from the unidentified soluble microbial products. Methane was not produced after the startup, and all PVA beads were not disintegrated. Results of a batch test showed that organic substrate was preferably consumed by the denitrify bacteria in favor of methane-producing bacteria. Scanning electron micrographs showed that most bacteria were populated on the bead surface due to the availability of nitrate and substrate.

Anoxic treatment of low-strength wastewater by immobilized sludge

Low levels of phenol and m-cresol were effectively removed from wastewater under anoxic condition using immobilized sludge. A 138-day experiment was conducted using wastewater containing NO3--N (22.3 mg·l-1), phenol (10 mg·l-1) and m-cresol (5 mg·l-1) at 30°C using sucrose (50 mg·l-1) as co-substrate in an upflow reactor packed with polyvinyl alcohol (PVA) beads entrapped with anoxic sludge and powdered activated carbon (PAC). Throughout the experiment, phenol and m-cresol in the effluent were below the detectable level of 1.0 mg·l-1 even when HRT (hydraulic retention time) was as low as 0.55 hour. The effluent quality in general decreased with HRT. At 5.9 hours of HRT, the reactor effluent contained 5.9 mg·l-1 of COD (chemical oxygen demand) and 1.3 mg·l-1 of NO3--N; but at 0.55 hour, they were, 17.3 and 5.7 mg·l-1, respectively. The effluent COD was from the unidentified soluble microbial products. Methane was not produced after the startup, and all PVA beads were not disintegrated. Results of a batch test showed that organic substrate was preferably consumed by the denitrify bacteria in favor of methane-producing bacteria. Scanning electron micrographs showed that most bacteria were populated on the bead surface due to the availability of nitrate and substrate.

Suppressive Effects of Calcium Polysulfide on Filamentous Bulking in Activated Sludge Process.

We investigated the suppressive effects on filamentous bulking by the addition of calcium polysulfide (CPS) . Laboratory experiments were conducted on three activated sludge systems with various loadings of CPS. The influent CPS in the three systems were 0, 100, and 200mg⋅l-1. All systems were operated under the same conditions, that is 0.24kg⋅m-3⋅day-1 of TOC volumetric loading rate, 24 hours of hydraulic retention time, temperature at 25°C, and were approximately operated at the same sludge loadings. A mixture of glucose and pepton was used as the substrate and easily caused the filamentous bulking. The mixed cultures developed in the systems mentioned possessed average SVI values of 400, 232, and 129ml⋅g-1 respectively. From microscopic and microbial observation, the high SVI value was caused by a high content of filamentous microorganisms in the developed mixed cultures. The series with CPS had different microflora compared with the control series with no loading of CPS. It was concluded that CPS suppressed the growth of filamentous microorganisms, and led to the growth of non-filamentous ones, i.e., Zooglea-like flocs.

Development of Technology for the Use of the UASB Reactor in Domestic Sewage Treatment

The lack of a simple and economic option for the treatment of sewage created the need to develop and make the UASB reactor adequate for low strength wastes. Thus a UASB reactor with 106 ℓ capacity was built, which was specially designed for sewage treatment. Several treatability tests were conducted with raw and settled domestic sewage, with only A hours of hydraulic retention time. This proved the reactor's technical feasibility in treating raw sewage at ambient temperature in São Paulo. Based on these experiments, the reactor was scaled up to 120 m3 and built for the treatment of raw sewage at ambient temperature. The operation is in its initial phase, and good COD removals are already being observed, although steady state has not been achieved yet. Since the cost of the system was extremely low, it is a feasible option to be applied in this country.