Effects of hydraulic retention time, temperature, and effluent recycling on efficiency of anaerobic filter in treating rural domestic wastewater

With rural population expansion and improvement of the socio-economic standard of living, treatment of rural domestic wastewater has rapidly become a major aspect of environmental concern. Selection of a suitable method for treatment of rural domestic wastewater depends on its efficiency, simplicity, and cost-effectiveness. This study investigated the effects of hydraulic retention time （HRT）, temperature, and effluent recycling on the treatment efficiency of an anaerobic filter （AF） reactor. The first round of experimental operations was run for three months with HRTs of one, two, and three days, temperatures of 18℃, 21℃, and 24℃, and no effluent recycling. The second round of experimental operations was conducted for another three months with HRTs of three and four days; temperatures of 30.67℃, 30.57℃, and 26.91 ℃ ; and three effluent recycling ratios of 1：1, 1：2, and 2：1. The first round of operations showed removal rates of 32% to 44% for COD, 30% to 35% for TN, 32% to 36% for NH4-N, 19% to 23% for NO3-N, and 12% to 22% for TE In the second round of operations, the removal rates varied from 75% to 81% for COD, 35% to 41% for TN, 31% to 39% for NH4-N, 30% to 34% for NO3-N, and 41% to 48% for TP. The average gas production rates were 6.72 L/d and 7.26 L/d for the first and second rounds of operations, respectively. The gas production rate increased in the second round of operations as a result of applied effluent recycling. The best removal efficiency was obtained for an optimum HRT of three days, a temperature of 30℃, and an effluent recycling ratio of 2：1. The results show that the removal efficiency of the AF reactor was affected by HRT, temperature, and effluent recycling.

Effect of Solid Retention and Hydraulic Retention Times on Membrane Fouling in Membrane Bioreactor

In this bench scale submerged membrane bioreactor, effect of solid retention time and hydraulic retention time on membrane fouling propensity has been studied. This experiment is carried out at different solid retention time of 5, 10, 30, 70 and 98 days; and fouling behavior of membrane bioreactor is investigated. Average effluent quality is found to be 88.14%-94.38%. The experiment with different hydraulic retention is carried for 3 to 4 days and fouling behavior has been investigated. The effluent quality at different hydraulic retention time of 1, 2, 3, 5, 10 and 24 hours has been investigated. This paper aims to search optimal values of solid and hydraulic retention times at which lower fouling and higher organic removal efficiency can be obtained. This study has been mainly focused on operating parameters rather than microbial structure, effect and analysis of activated sludge to membrane fouling.

Determination and discussion hydraulic retention time in membrane bioreactor system

Based on the microorganism kinetic model, the formula for computing hydraulic retention time in a membrane bioreactor system (MBR) is derived. With considering HRT as an evaluation index a combinational approach was used to discuss factors which have an effect on MBR. As a result, the influencing factors were listed in order from strength to weakness as: maximum specific removal rate K , saturation constant K s, maintenance coefficient m , maximum specific growth rate μ m and observed yield coefficient Y obs . Moreover, the formula was simplified, whose parameters were experimentally determined in petrochemical wastewater treatment. The simplified formula is θ=1.1(1/β-1)(K s +S)/KX 0, for petrochemical wastewater treatment K and K s equaled 0 185 and 154.2, respectively.

Effects of hydraulic retention time on net present value and performance in a membrane bioreactor treating antibiotic production wastewater

A cost sensitivity analysis was performed for an industrial membrane bioreactor to quantify the effects of hydraulic retention times and related operational parameters on cost.Different hydraulic retention times(72-24 h)were subjected to a flat-sheet membrane bioreactor updated from an existing 72 h oxidation ditch treating antibiotic production wastewater.Field experimental data from the membrane bioreactor,both full-scale(500 m/d)and pilot(1.0 m3/d),were used to calculate the net present value(NPV),incorporating both capital expenditure(CAPEX)and operating expenditure.The results showed that the tank cost was estimated above membrane cost in the 38.2%,where capital expenditure contributed 24.2%more than operational expenditure.Tank construction cost was decisive in determining the net present value contributed 62.1%to the capital expenditure.The membrane bioreactor has the advantage of a longer lifespan flat-sheet membrane,while flux decline was tolerable.The antibiotics decreased to 1.87±0.33 mg/L in the MBR effluent.The upgrade to the membrane bioreactor also benefited further treatments by 10.1%-44.7%lower direct investment.

Modelling the thresholds of nitrogen/phosphorus concentration and hydraulic retention time for bloom control in reclaimed water landscape

The risks posed by algal blooms caused by nitrogen and phosphorus in reclaimed water used in urban water landscapes need to be carefully controlled.In this study,the combined effects of the nitrogen and phosphorus concentrations and the light intensity and temperature on the specific growth rates of algae were determined using Monod,Steele,and Arrhenius models,then an integrated algal growth model was developed.The algae biomass,nitrogen concentration,and phosphorus concentration mass balance equations were used to establish a new control model describing the nitrogen and phosphorus concentration and hydraulic retention time thresholds for algal blooms.The model parameters were determined by fitting the models to data acquired experimentally.Finally,the control model and numerical simulations for six typical algae and mixed algae under standard conditions were used to determine nitrogen/phosphorus concentration and hydraulic retention time thresholds for landscape water to which reclaimed water is supplied(i.e.,for a reclaimed water landscape).

Study on Purification Efficiency of Vertical Flow Wetlands on Domestic Wastewater

The combination method of intermittent influent and vertical flow wetlands （VFW） was used in the test to treat the domestic wastewater. Four artificial wetlands including Typha latifolia wetland,Phragmites australis （P.H.） wetland,polyculture wetlands （Typha latifolia and Phragmites australis） and non-vegetation wetland were established in the test. The effects of hydraulic retention time （HRT） and plant species on pollutants removal efficiencies were studied. The results showed that when HRT=7,the treatment efficiencies of wetlands with plants for the removal of TN and NH＋4-N were up to 99.65% and 99.58%,respectively. For the control wetland,TN removal efficiency was up to 87.9% when HRT were 6 days,and NH＋4-N removal efficiency was up to 91.8% when HRT were 5 days. TP removal efficiencies of four wetlands were higher than 93% when HRT was 6 days. Through the studies on different plants,it was found that vegetation wetlands had better nitrogen removal efficiency than non-vegetation wetland. The treatment efficacy of Phragmites australis wetland and polyculture wetland was better than Typha latifolia wetland.

Feasibility and simulation model of a pilot scale membrane bioreactor for wastewater treatment and reuse from Chinese traditional medicine

The lack and pollution of water resource make wastewater reuse necessary. The pilot scale long-term tests for submerged membrane bioreactor were conducted to treat the effluents of anaerobic or aerobic treatment process for the high-strength Chinese traditional medicine wastewater. This article was focused on the feasibility of the wastewater treatment and reuse at shorter hydraulic retention time （HRT） of 5.0, 3.2 and 2.13 h. MLSS growth, membrane flux, vacuum values and chemical cleaning periods were also investigated. The experimental results of treating two-phase anaerobic treatment effluent demonstrated that the CODfilt was less than 100 mg/L when the influent COD was between 500-10000 mg/L at HRT of 5.0 h, which could satisfy the normal discharged standard in China. The experimental results to treat cross flow aerobic reactor effluent demonstrated that the average value of CODfilt was 17.28 mg/L when the average value of influent COD was 192.84 mg/L at HRT of 2.13 h during 106 d, which could completely meet the normal standard for water reuse. The maximum MLSS and MLVSS reached 24000 and 14500 mg/L at HRT of 3.2 h respectively. Membrane flux had maximal resume degrees of 94.7% at vacuum value of 0.02 MPa after cleaning. Chemical cleaning periods of membrane module were 150 d. A simulation model of operational parameters was also established based on the theory of back propagation neural network and linear regression of traditional mathematical model. The simulation model showed that the optimum operational parameters were suggested as follows： HRT was 5.0 h, SRT was 100 d, the range of COD loading rate was between 10.664-20.451 kg/（m3.d）, the range of MLSS was between 7543-13694 mg/L.

Using a zeolite medium biofilter to remove organic pollutant and ammonia simultaneously

A pilot scale zeolite medium biological aerated filter(ZBAF) was designed and used to treat municipal wastewater. It showed that ZBAF could simultaneously remove chemical oxygen demand(COD), ammonia-N and turbidity to satisfied degree at a hydraulic retention time(HRT) of 0.95 h. Their average removal efficiencies were 73.9%, 88.4% and 96.2% with the corresponding average effluent concentrations of 43.4 mg/L, 3.5 mg/L and 3.7 NTU, respectively. These effluent items met with the water quality standard of the treated water reused for cooling water. The COD removal volumetric loading rate increased proportionally with its applied volumetric loading rate with its maximum of 7.1 kg/(m 3·d). Ammonia-N removal loading rate also increased proportionally with its applied loading rate at HRT of longer than 0.95 h and the feasible maximum removal loading rate was 0.9 kg/(m 3·d). The COD loading rate did not affect the ammonia-N removal efficiency significantly when it was lower than 5.5 kg/(m 3·d). ZBAF has good application prospect for its low cost and high removal efficiency in the future.

Effectiveness of a Subsurface Constructed Wetland on the Treatment of Saline Wastewater

This study evaluated the capability of a constructed wetland for treating saline wastewater. A pilot-scale constructed wetland system was set up and was initially operated at low, then increasing salt levels to determine the effect of salinity on the contaminants＇ removal performance. The effect of hydraulic retention time （HRT） variation on treatment efficiency of the reed wetland was also discussed. Average removal efficiencies of the reed （Phragmites australis） wetland were found to be 79.0% for COD, 72.2% for ammonia nitrogen （NH3-N） and 82.8% for total phosphorus （TP）. Reed planting had obvious improvement on COD and NH3-N removal efficiency when compared to an unplanted system. With the seawater proportion in the influent increasing from 20% to 30%, the TP removal efficiency improved obviously. COD removal efficiency of the reed wetland was positively correlated with HRT under high salinity condition, while excess HRT had adverse impacts on the NH3-N and TP removal. Optimal HRT for NH3-N and TP removal was 4 days. Results obtained can be beneficially used to improve the use of constructed wetlands in saline wastewater treatment.

In-depth observations of fermentative hydrogen production from liquid swine manure using an anaerobic sequencing batch reactor

In this study,experiments were designed to reveal in-depth information of the effect of pH and hydraulic retention time（HRT）on biohydrogen fermentation from liquid swine manure supplemented with glucose using an Anaerobic Sequencing Batch Reactor（ASBR）System.Five values of HRT（8,12,16,20,and 24 h）were first tested and the best HRT determined was further studied at five p H levels（4.4,4.7,5.0,5.3,and 5.6）.The results showed that for HRT 24 h,there was a dividing H2 content（around 37%）related to the total biogas production rate for the ASBR System running at p H 5.0.When the H2 content went beyond 37%,an appreciable decline in biogas production rate was observed,implying that there might exist an H2 content limit in the biogas.For other HRTs（8 through 20 h）,an average H2 content of 42%could be achieved.In the second experiment（HRT 12 h）,the highest H2 content（35%）in the biogas was found to be associated with p H 5.0.The upswing of p H from 5.0 to 5.6 had a significantly more impact on biogas H2 content than the downswing of p H from5.0 to 4.3.The results also indicated good linear relationships of biogas and H2 production rates with HRT（r=0.9971 and0.9967,respectively）.Since the optimal ASBR operating conditions were different for the biogas/H2 production rates and the H2 yield,a compromised combination of the running parameters was determined to be HRT 12 h and pH 5.0 in order to achieve good biogas/H2 productions.

Performance of Experimental Bio-Digestion for Pathological and Biodegradable Waste Management at Mwananyamala Regional Referral Hospital Tanzania

The aim of the experimental trial was to evaluate the performance of the designed placenta and other pathological waste digester system on the effectiveness of digesting the placenta and its energy recovery (bio-gas) process in Mwananyamala Referral Hospital in Dar es Salaam. A 32 m3 digester is constructed in Mwananyamala Referral Hospital, one inlet of which is to attach to the toilet of maternity ward, where the placentas are flushed directly into the digester, while food waste is fed through another inlet. The slurry of the digester is sent to a sewer/septic tank to avoid further handling. Most fraction of the waste fed into the digester is food waste. In general with the amount of 25.6 ± 4.5 kg/day of placenta and 83.1 ± 14.7 kg/day of food waste, 2.5 m3/d gas was produced. The pH throughout the study period (that is of 18 weeks) was found to be consistent within the range of 6.3 to 8.0, while the pressure ranged from 5 kPa - 33 kPa. Average temperature within the digester was found to be 30.3°C. With all the favorable condition, gas production was consistent and hence the system has been successful in management of the pathological waste along with the production of gas as an alternative source of energy for the hospital.

Hydrodynamic behaviour of the lateral flow biological aerated filter

Pulsed signal experiment was carried out to determine the hydrodynamic behaviours of lateral flow biological aerated filter(LBAF). With the analysis of experimental results, LBAF is viewed as an approximate plug flow reactor, and hydraulic retention time distribution function was derived based on LBAF. The results show that flow rate and aeration strength are two critical factors which influence flow patterns in LBAF reactor. The hydrodynamic behaviour analysis of LBAF is the theoretical basis of future research on improving capacity factor and developing kinetic model for the reactor.

Treatment of Domestic Sewage by Two-Stage-Bio-Contact Oxidation Process

Effects of hydraulic retention time (HRT ) and gas volume on efficiency of wastewater treatment are dis- cussed based on a simulation experiment in which the domestic swage was treated by the two-stage-bio-contact oxida- tion process. The result shows that the average CODCr, BOD5 , suspended solid (SS), and ammonia-nitrogen removal rate are 94.5 %, 93.2 %, 91.7 % and 46.9 %, respectively, under the conditions of a total air/water ratio of 5∶1 , an air/water ratio of 3:1 for oxidation tank 1 and 2:1for oxidation tank 2and a hydraulic retention time of 1 h for each stage. This method is suitable for domestic sewage treatment of residential community and small towns as well.

Waste activated sludge treatment based on temperature staged and biologically phased anaerobic digestion system

The concept of temperature staged and biological phased （TSBP） was proposed to enhance the performance of waste-activated sludge anaerobic digestion. Semi-continuous experiments were used to investigate the effect of temperature （35 to 70℃） as well as the hydraulic retention time （HRT） （2, 4 and 6 days） on the acidogenic phase. The results showed that the solubilization degree of waste- activated sludge increased from 14.7% to 30.1% with temperature increasing from 35 to 70℃, while the acidification degree was highest at 45℃ （17.6%）, and this was quite different from the temperature impact on hydrolysis. Compared with HRT of 2 and 6 days, 4 days was chosen as the appropriate HRT because of its relatively high solubilization degree （24.6%） and acidification degree （20.1%） at 45℃. The TSBP system combined the acidogenic reactor （45℃, 4 days） with the methanogenic reactor （35℃, 16 days） and the results showed 84.8% and 11.4% higher methane yield and volatile solid reduction, respectively, compared with that of the single-stage anaerobic digestion system with HRT of 20 days at 35℃. Moreover, different microbial morphologies were observed in the acidogenic- and methanogenic-phase reactors, which resulted from the temperature control and HRT adjustment. All the above results indicated that 45℃ was the optimum temperature to inhibit the activity of methanogenic bacteria in the acidogenic phase, and temperature staging and phase separation was thus accomplished. The advantages of the TSBP process were also confirmed by a full-scale waste-activated sludge anaerobic digestion project which was an energy self-sufficient system.

Pre-treatment of pyridine wastewater by new cathodic–anodic-electrolysis packing

A novel cathodic–anodic-electrolysis packing（CAEP） used in the treatment of pyridine wastewater was researched, which mainly consisted of 4,4′-diamino-2,2′-disulfonic acid（DSD acid） industrial iron sludge. The physical properties and morphology of the packing were studied. The CAEP was used in a column reactor during the pretreatment of pyridine wastewater. The influence of p H, hydraulic retention time（HRT）, the air–liquid ratio（A/L）and the initial concentration of pyridine were investigated by measuring the removal of total organic carbon（TOC） and pyridine. The characterization results showed that the bulk density, grain density, water absorption percentage and specific surface area were 921 kg/m3,1086 kg/m3, 25% and 29.89 m^2/g, respectively; the removal of TOC and pyridine could reach50% and 58% at the optimal experimental conditions（p H = 3, HRT = 8 hr, A/L = 2）. Notably,the surface of the packing was renewed constantly during the running of the filter, and the handling capacity was stable after running for three months.

Anaerobic digestion of cyanobacteria and chlorella to produce methane for biofuel

The methane potentials of cyanobacteria and chlorella have been investigated in eight different lab scale reactors at 25℃for three-day Hydraulic Retention Time(HRT).Autoclavation pre-treatment was applied to the cyanobacteria to aid digestion,while the Chlorella was obtained and digested in powdery form.The organic loading rates were 1g VS,2 g VS,3 g VS,4 g VS,5 g VS,6 g VS,7 g VS,8 g VS and 9 g VS.Methane production rates increased with increasing loading rates and started declining at loading rate higher than 7 g VS,while the HRT was kept constant.The highest methane production rates for cyanobacteria and chlorella were(78±25)mL/(L·d)and(100±25)mL/(L·d),respectively,at loading rate of 7 g VS.Digester instability occurred at loading rates of 8 g VS and 9 g VS with higher accumulation of methane concentrations.Lipid compositions of both feeds were close and the methane production potentials of both biomasses were also close and followed the same trend.

Pre-treatment of mscanthus sinensis with Bacta-sile to aid anaerobic digestion

The investigation of the biodegradability and methane potential of bacterial pre-treated miscanthus sinensis has been carried out.One percent solution of Bacta-sile:A silage promoter was used to pre-treat miscanthus sinensis at 25℃.The anaerobic digestion experiments were carried out at 25℃ and 35℃ in batch experiments.The organic loading rates(OLR)varied between 1.25 g and 7 g in different batch reactors.The results showed that the highest methane concentration was 57% from digester 1 while the lowest methane produced was 38% from digester 3.The low methane production from digester 3 was attributed to temperature changes and poor organic loading rate.Bacterial pretreatment aided biodegradation of miscanthus at 25℃.Operating temperature of 25℃ had a great effect on digestion experiments resulting to longer required Hydraulic Retention Time(HRT).

Treatment of Aniline-Contaminated Wastewater by Sequencing Biofilm Batch Reactor System Under Micro-Aerobic Condition

Sequencing biofilm batch reactor(SBBR) under micro-aerobic condition was applied to the treatment of aniline-contaminated wastewater in this study.Hydraulic retention time(HRT) of 12—36 h and dissolved oxygen(DO) concentration of 0.1—0.5 mg/L were selected as the operating variables to model,analyze and optimize the process.Five dependent parameters,aniline(AN),chemical oxygen demand(COD),ammonium,total nitrogen(TN) and total phosphorus(TP) removal efficiencies as the process responses,were studied.From the results,increase in DO concentration could promote the AN,COD and ammonium removal;increase in HRT could also lead to increase of the AN and ammonium removal,but might decrease COD removal due to endogenous respiration and soluble microbial products.In the SBBR system,24 h for HRT and 0.5 mg/L for DO concentration were chosen as the optimum operating condition.The actual removal efficiencies of COD,AN and ammonium under the optimum operating condition were 98.37%,100%and 89.29%,respectively.The experimental findings were in close agreement with the model prediction.The presence of glucose could promote bacterial growth and has positive influence on AN degradation and ammonium removal.