Low-strength Domestic Wastewater Research Articles

Achieving nitrite accumulation in a continuous system treating low-strength domestic wastewater: switchover from batch start-up to continuous operation with process control

Although biological nitrogen removal via nitrite is recognized as one of the cost-effective and sustainable biological nitrogen removal processes, nitrite accumulation has proven difficult to achieve in continuous processes treating low-strength nitrogenous wastewater. Partial nitrification to nitrite was achieved and maintained in a lab-scale completely stirred tank reactor (CSTR) treating real domestic wastewater. During the start-up period, sludge with ammonia-oxidizing bacteria (AOB) but no nitrite-oxidizing bacteria (NOB) was obtained by batch operation with aeration time control. The nitrifying sludge with the dominance of AOB was then directly switched into continuous operation. It was demonstrated that partial nitrification to nitrite in the continuous system could be repeatedly and reliably achieved using this start-up strategy. The ratio of dissolved oxygen to ammonium loading rate (DO/ALR) was critical to maintain high ammonium removal efficiency and nitrite accumulation ratio. Over 85% of nitrite accumulation ratio and more than 95% of ammonium removal efficiency were achieved at DO/ALR ratios in an optimal range of 4.0-6.0mg O(2)/gN d, even under the disturbances of ammonium loading rate. Microbial population shift was investigated, and fluorescence in situ hybridization analysis indicated that AOB were the dominant nitrifying bacteria over NOB when stable partial nitrification was established.

Partial Nitrification to Nitrite with Real-Time Aeration Duration Control in an SBR Treating Domestic Wastewater

Sustainable partial nitrification to nitrite has been proven difficult in treating low strength nitrogenous wastewater. Real-time aeration duration control was used to achieve efficient partial nitrification to nitrite in a sequencing batch reactor (SBR) to treat low strength domestic wastewater. Above 95% nitrite accumulation ratio was maintained for long-term operation at normal condition. Partial nitrification established by controlling aeration duration showed good performance and robustness even though some time encountering long-term extended aeration. Process control enhanced the successful accumulation of ammonia oxidizing bacteria (AOB) and washout of nitrite oxidizing bacteria (NOB).

Simultaneous nutrients and carbon removal from low-strength domestic wastewater with an immobilised-microorganism biological aerated filter

To improve the efficiency of low-strength domestic wastewater treatment, an immobilised-microorganism biological aerated filter (I-BAF) was established for simultaneous carbon, nitrogen and phosphorus removal. The I-BAF performance was systematically evaluated under continuous and intermittent aeration modes. At the optimal condition with an intermittent aeration control schedule of 2 h on/1 h off, the maximum removal rates of COD, NH(4)(+)-N, TN and P were 82.54%, 94.83%, 51.85% and 61.49%, respectively, and the corresponding averaged effluents could meet the first class standards of China. Further analysis of PCR-DGGE profile revealed that members of the gamma and alpha proteobacterium bacterial groups were probably responsible for the nitrogen and phosphorus removal. The I-BAF system showed excellent performance in carbon and nutrients removal, which provided a cost-effective solution for the treatment of low-strength domestic wastewater.

Short- and long-term effects of temperature on partial nitrification in a sequencing batch reactor treating domestic wastewater

Partial nitrification to nitrite has been frequently obtained at high temperatures, but has proved difficult to achieve at low temperatures when treating low strength domestic wastewater. In this study, the long-term effects of temperature on partial nitrification were investigated by operating a sequencing bath reactor with the use of aeration duration control. The specific ammonia oxidation rate decreased by 1.5 times with the temperature decreasing from 25 to 15 °C. However, low temperature did not deteriorate the stable partial nitrification performance. Nitrite accumulation ratio was always above 90%, even slightly higher (above 95%) at low temperatures. The nitrifying sludge accumulated with ammonia-oxidizing bacteria (AOB), but washout of nitrite-oxidizing bacteria (NOB) was used to determine the short-term effects of temperature on ammonia oxidation process. The ammonia oxidation rate depended more sensitively on lower temperatures; correspondingly the temperature coefficient θ was 1.172 from 5 to 20 °C, while θ was 1.062 from 20 to 35 °C. Moreover, the larger activation energy (111.5 kJ mol −1) was found at lower temperatures of 5–20 °C, whereas the smaller value (42.0 kJ mol −1) was observed at higher temperatures of 20–35 °C. These findings might be contributed to extend the applicability of the partial nitrification process in wastewater treatment plants operated under cold weather conditions. It is suggested that the selective enrichment of AOB as well as the washout of NOB be obtained by process control before making the biomass slowly adapt to low temperatures for achieving partial nitrification to nitrite at low temperatures.

Biomass production of papyrus ( Cyperus papyrus) in constructed wetland treating low-strength domestic wastewater

In this study, the pilot-scale constructed wetlands were fed with low-strength domestic wastewater to investigate the energy-capturing efficiency and plant productivity. Papyrus was a selected emergent macrophyte planted in the systems. The wastewater was intermittently fed to the systems, corresponding to the organic loading rates of 10, 16, 31, and 63 kg BOD/ha-d. With abundant sunshine in the tropical-climate area, papyrus converted solar radiation to biomass of about 2200–3100 g dry weight/m 2 from the two-month period of the experiments. Furthermore, the energy contents of papyrus are 16.2, 17.2, and 16.8 MJ/kg for culms, umbels, and total above-ground parts, respectively. From the plant productivity and the energy contents of papyrus obtained from this study, the energy capturing efficiencies can be estimated to be in the range of 4.4–6.0%, which are relatively high, compared with those of other plants.

Effective and robust partial nitrification to nitrite by real-time aeration duration control in an SBR treating domestic wastewater

Achieving sustainable partial nitrification to nitrite has been proven difficult in treating low strength nitrogenous wastewater. Real-time aeration duration control was used to achieve efficient partial nitrification to nitrite in a sequencing batch reactor (SBR) to treat low strength domestic wastewater. Above 90% nitrite accumulation ratio was maintained for long-term operation at normal condition, or even lower water temperature in winter. Partial nitrification established by controlling aeration duration showed good performance and robustness even though encountering long-term extended aeration and starvation period. Process control enhanced the successful accumulation of ammonia oxidizing bacteria (AOB) and washout of nitrite oxidizing bacteria (NOB). Scanning electron microscope observations indicated that the microbial morphology showed a shift towards small rod-shaped clusters. Fluorescence in situ hybridization (FISH) results demonstrated AOB were the dominant nitrifying bacteria, up to 8.3 ± 1.1% of the total bacteria; on the contrary, the density of NOB decreased to be negligible after 135 days operation since adopting process control.

Effect of thermochemical sludge pretreatment on sludge reduction and on performances of anoxic‐aerobic membrane bioreactor treating low strength domestic wastewater

AbstractBACKGROUND: Reduction of excess sludge production has become an urgent issue. An investigation into the influence of thermochemical sludge pretreatment on sludge reduction in a bench‐scale anoxic‐aerobic membrane bioreactor was performed. Two systems were operated. In one system, part of the mixed liquid (1.5% of the influent flow rate) was pretreated thermochemically (at 80 °C, pH 11 and 3 h) and returned to the bioreactor. This study examined and evaluated the effect of thermochemical sludge pretreatment on the reduction of excess sludge and on the performance of the system.RESULTS: The average solubilization efficiency of the pretreated sludge was found to be about 0.2. The sludge production rate of the experimental system (E‐MBR) was less than that of the control (C‐MBR) by about 33%. The total phosphorus was removed mainly by normal cell synthesis, with removal efficiencies of 38–40% and 40–42% for the E‐MBR and C‐MBR, respectively. The total nitrogen removal in the E‐MBR was slightly higher than in the C‐MBR due to supply of soluble chemical oxygen demand (SCOD) from the digested sludge solution as an external carbon source. The mixed liquor volatile suspended solids (MLVSS) and mixed liquor suspended solids (MLSS) ratios for the two systems were almost identical, in the range 74–77%, indicating that the inorganics from the disintegrated cells do not accumulate as particulates in the reactor. The TMP was maintained at less than 6 cmHg for 180 days without membrane cleaning.CONCLUSION: Thermochemical sludge pretreatment can play an important role in reducing sludge production. The qualities of the effluent water were not significantly affected during 6 months of operation. Copyright © 2009 Society of Chemical Industry

Treatment of low and medium strength sewage in a lab-scale gradual concentric chambers (GCC) reactor

One of the major challenges of anaerobic technology is its applicability for low strength wastewaters, such as sewage. The lab-scale design and performance of a novel Gradual Concentric Chambers (GCC) reactor treating low (165+/-24 mg COD/L) and medium strength (550 mg COD/L) domestic wastewaters were studied. Experimental data were collected to evaluate the influence of chemical oxygen demand (COD) concentrations in the influent and the hydraulic retention time (HRT) on the performance of the GCC reactor. Two reactors (R1 and R2), integrating anaerobic and aerobic processes, were studied at ambient (26 degrees C) and mesophilic (35 degrees C) temperature, respectively. The highest COD removal efficiency (94%) was obtained when treating medium strength wastewater at an organic loading rate (OLR) of 1.9 g COD/L.d (HRT = 4 h). The COD levels in the final effluent were around 36 mg/L. For the low strength domestic wastewater, a highest removal efficiency of 85% was observed, producing a final effluent with 22 mg COD/L. Changes in the nutrient concentration levels were followed for both reactors.

COD removal and nitrification of low-strength domestic wastewater in aerobic granular sludge sequencing batch reactors

Acetate-fed granules were used to start-up reactors for the treatment of low-strength domestic wastewater at 25 °C (R1) and 35 °C (R2). Two hundred milligrams per liter COD in domestic wastewater was easily removed. Granular seeds acclimated to NH 4 +-N removal after domestic wastewater was used and the specific NH 4 +-N removal rate increased linely after 7-day operation. Effluent NH 4 +-N was below 5 mg l −1 and NH4 +-N removal efficiency increased to above 90% after 22-day operation with cycle time of 2 h in both reactors with 0.3 kg m −3 day −1 NH 4 +-N loading rate. In addition, granular seeds cultivated at 25 °C showed good adaptation to higher temperature and the granules in R2 at 35 °C showed good stability in 4-month operation.

Removal of carbon and nutrients from low strength domestic wastewater by expanded granular sludge bed-zeolite bed filtration (EGSB-ZBF) integrated treatment concept

The performance of an expanded granular sludge bed (EGSB) reactor coupled with zeolite bed filtration (ZBF) for treating low strength domestic wastewater was monitored at 35 °C for 7 months. The whole operation period of EGSB system was divided into five phases. Each phase ran at up-flow velocity (m/h) of 0.51, 1.02, 3.57, 2.05, 9.69, and hydraulic retention time (HRT) (h) of 6, 3, 0.87, 1.5, 0.32, respectively. The influent chemical oxygen demand (COD) was kept approximate at 150 ± 100 mg/L. Under these conditions, the COD removal efficiency of using EGSB system in five phases reached to 81.08, 57.94, 82.79, 56.58 and 79.52%, respectively. Moreover, since nutrients such as NH 4 + and PO 4 3− were only removed to a limited extent by EGSB, additional treatment is required. The ZBF was employed in phase 2 as a post-treatment following EGSB. NH 4 + and PO 4 3− concentrations were decreased by 100%, respectively, in the first 2 or 3 d using fresh zeolite. The simple design and excellent treatment performance indicated that this system could be used as a novel Sewage Integrated Treatment System (SITS) for developing country especially in a tropical area.

Carbon and nitrogen removal from low-strength domestic wastewater with a two-stage submerged biological filter

The aim of the present study was to evaluate the secondary and tertiary treatment of low -strength domestic wastewater with submerged biological filters (BFs). The experiments were carried out with a two-stage pilot plant consisting of two subsequent filter columns. In the first aerated reactor, the removal of carbon and nitrification was accomplished (secondary nitrification); while, in the second anoxic reactor a post-denitrification process with methanol as external carbon source was performed. During the 3 months of experimental period, in average terms, Total Suspended Solids (TSS) concentrations of 156 mg/L were reduced to 5 mg/L; Chemical Oxygen Demand (COD) concentrations of 179 mg/L were reduced to 43 mg/L. In the secondary nitrification, mean influent NH4 + concentrations of 6.1 mg/L were reduced to average values of 1.8 mg/L. During the post-denitrification, mean influent NO3 − concentrations of 12.0 mg/L were reduced to average values of 6.1 mg/L. The overall process produced a backwashing effluent with an average concentration of about 175 mg/L of TSS.

Stimulation of Methanogenesis in a Laboratory Scale UASB Reactor Treating Domestic Sewage by Fe(0) Application

The effects of application of zero valence Fe (Fe(0)) on the anaerobic digestion of sewage was investigated using two laboratory scale UASB reactors. One reactor had Fe(0) addition in a container found midway along the recycling loop. The other one was a control reactor. In a test run period of 76 days, the Fe(0) application significantly increased the CH 4 yield by 8.7% and decreased the effluent COD concentration by 21.0% relative to the control reactor. A decrease of the H2 concentration of biogas and the CODs/CODt ratio in effluent by Fe(0) application were observed. The obtained results imply that the methanogenesis and COD removal efficiency of the UASB reactor were stimulated by Fe(0) application. The higher performance of the reactor with Fe(0) application arises from the integrated functions of Fe(0) or its ionic state as donor of H2, macronutrient, and flocculant. This study showed that the supply of Fe(0) to a UASB can improve the methanogenesis and the overall COD removal of a UASB reactor treating low-strength domestic waste water.

Combined Carbonaceous Removal and Nitrification with Biological Aerated Filters

This paper describes the use of a submerged biological aerated filter (BAFs), on a pilot plant scale, in the secondary nitrification of low strength domestic wastewater. The results, obtained throughout three months of tests, confirmed the ability of BAFs to obtain simultaneous carbonaceous removal and nitrification. In fact, after a start-up period of 5 weeks, a remarkable steady state condition in the removal of suspended solids (TSS), chemical oxygen demand (COD) and nitrification was reached. For a hydraulic loading rate of 1.6 m3 m−2 h−1, the mean efficiency of the process in the removal of TSS and COD was 85% and 83% respectively. Mean concentrations in the influent flow of around 114 mgTSS/L and 140 mgCOD/L were reduced to average values of below 17 mgTSS/L and 25 mgCOD/L. Secondary nitrification was achieved with a mean efficiency of 85% for a mean volumetric loads of 0.45 kgN-Namm m−3 d−1 (25°C). Through an intensive activity of nitrification, in the steady state condition, mean influent concentrations of around 12 mgN-Namm/L were reduced to average values of below 2 mgN-Namm/L. The removal loading rate increased linearly with the applied loading rate for volumetric loads of up to 0.7 kgN-Namm m−3 d−1. The nitrification was not sensitive to the applied COD loads because of the low level of carbon substrate.

Anaerobic treatment of domestic wastewater in temperate climates: treatment plant modelling with economic considerations

Although research suggests that anaerobic treatment of low-strength domestic wastewater is possible in temperate climates, to date, full-scale applications have only been pioneered in hot regions. However, burgeoning environmental legislation in developed countries is giving the impetus to develop anaerobic wastewater treatment systems due to potential economic and environmental benefits they hold over traditional aerobic techniques. In this paper a design rationale for low-temperature, low-strength (COD <1000 mg l −1), two-phase anaerobic wastewater treatment is developed through empirical modelling of data from published research, and from assumptions arising from a literature review. Model calculations are applied to typical domestic sewage characteristics at two different flow rates, based on population equivalents. Results indicate that soluble COD production in the model hydrolytic tank are similar to those achieved in pilot scale plants in the Netherlands. Model anaerobic reactor sludge characteristics are similar to those achieved in pilot and full-scale anaerobic reactors treating low-strength wastewaters. Indicative cost figures for a two-phase anaerobic treatment plant are given, but are incomplete without an assessment of the cost of post-treatment processes. Anaerobic treatment is likely to become more attractive in the future as new legislation relating to sludge disposal and renewable energy generation are introduced.

Nutrient removal from low strength domestic wastewater in sequencing batch biofilm reactor

Nutrient removal was investigated in a packed bed column, which was operated by changing of aerated and non-aerated periods. Good removal efficiencies for nitrogen and phosphorus were obtained at long aeration period. Highest nitrification efficiency was observed in run3 because the aeration period was enough to allow nitrification. NO3 concentration was not significantly changed during the cycle, because of simultaneous denitrification during aerobic stage. Nitrogen and phosphorus removal efficiencies reached to 71 and 74% in run3 respectively. Effluent concentrations of TKN, Tot.P, NH4 and NO3 were found as 3.8, 3, 1 and 2.5 mg/l respectively.

Anaerobic Treatment of Low-Strength Domestic Wastewater Using an Anaerobic Expanded Bed Reactor

A significant potential exists to lower energy consumption and reduce sludge production by incorporating anaerobic processes into wastewater treatment trains. The specific treatment arrangement studied in this case is the anaerobic treatment of primary clarifier effluent of wastewater treatment plants. Anaerobic batch assays showed that the primary clarifier effluent used in this study was ultimately 90% or more anaerobically biodegradable, thus suitable for anaerobic treatment. The anaerobic expanded bed reactor (AEBR) performed well over a wide range of influent CODs and temperatures, especially under severe conditions (5°C and 50 mg/L influent COD). The most efficient treatment was obtained with HRTs of three to six hours and influent COD of approximately 150 mg/L. Start-up of the reactor took about 60 days at 30°C and 80 days at 20°C.

Household Membrane Bioreactor in Domestic Wastewater Treatment

The activated sludge process coupled with hollow fiber membrane for solid-liquid separation was applied to treat low strength domestic wastewater. Pilot-scale experimental unit used in this study consisted of 2 modules of 0.03 μm pore size with 9 m2 surface area each, immersed in the reactor which has a maximum working volume of 1.5 m3. Even when sewage was fed at varying rates following its diurnal flow variation to the bioreactor, good stability of the process was achieved which was shown by the consistency in treated water quality. The effluent turbidity and COD were well within the limits (less than 0.5 NTU and 3-5 mg/L). The transmembrane pressure drop was less than 20 cm Hg even after 2 months of operation. Application of jet aeration could be used to prolong the operational life of the membrane in the bioreactor. This system is an ideal one to be used as household wastewater treatment system.

Treatment of low strength domestic wastewater using the anaerobic filter: by H. A. Kobayashi, M. K. Stenstrom and R. A. Mah

Treatment of low strength domestic wastewater using the anaerobic filter: by H. A. Kobayashi, M. K. Stenstrom and R. A. Mah

Treatment of low strength domestic wastewater using the anaerobic filter

A laboratory scale anaerobic filter packed with synthetic high surface area trickling filter media was used to treat a low strength domestic wastewater averaging 288 mg 1 −1 COD. The filter was operated for 60 days after reaching steady-state at 20, 25, 35°C at a loading rate of 0.02 lb COD ft −3 day −1 and 24 h hydraulic retention time. Filter effluent BOD 5 averaged 38 mg 1 −1 providing an average removal rate of 79%, and effluent COD averaged 78 mg 1 −1, corresponding to a 73% removal rate. Removal efficiencies showed very little sensitivity to daily fluctuations in influent wastewater quality. The filter performance at 25 and 35°C was not significantly different, but BOD and TSS removal efficiency declined a: 20°C. Gas production averaged 0.027 ft −3 of gas per ft 3 of influent wastewater, or 1.875 ft 3 of gas per pound of influent COD. Gas composition averaged 30% nitrogen, 65% methane, and 5% carbon dioxide. Ammonia nitrogen and sulfides both increased during treatment. It is concluded that the anaerobic filter is a promising candidate for treatment of low strength wastewaters and that post treatment for sulfides and ammonia may be necessary.