Optimum Hydraulic Retention Time Research Articles

Integrated fate assessment of aromatic amines in aerobic sewage treatment plants

The fate and exposure of chemicals in sewage treatment plants (STPs) are major considerations in risk assessment and environmental regulation. The biodegradability and removal of seven aromatic amines were systematically evaluated using a three-tiered integrated method: a standard ready biodegradability test, an aerobic sewage treatment simulation method, and model prediction. In tier 1, the seven aromatic amines were not readily biodegraded after 28 days. In adapted aerobic active sludge, 4-isopropyl aniline, 2,4-diaminotoluene, and 4-nitroaniline among them exhibited the degradation half-life time less than 20 h, the other four aromatic amines exhibited persistent with degradation half-life of > 60 h. In tier 2 of the aerobic sewage treatment simulation testing, 2,4-diaminotoluene, 4-nitroaniline, and 4-isopropylaniline demonstrated moderately to high overall removal. Hydraulic retention time (HRT) affects the removal with the optimum HRT was determined to be 12 h to 24. 2,6-Dimethyl aniline, 2-chloro-4-nitroaniline, 2,6-diethylaniline, and 3,4-dichloroaniline were not removed during the test, indicting these four aromatic amines will enter surface water and hence pose a potential risk to aquatic ecology. Considering the lack of an STP model in China for regulation purposes, in tier 3, we developed a Chinese STP (aerobic) (abbreviated as C-STP(O)) model that reflects a universal scenario for China to predict the fate. The predicted degradation, volatilization, and absorption showed a close relationship to the physicochemical properties of the chemicals, and had same tendency with tier 2 simulation test. The prediction showed that biodegradation rather than absorption or volatilization was the main removal process of aromatic amines in aerobic STP. With the combination of modified kinetics test with C-STP (O) model, the chemical fate can be more accurately predicted than using only the readily biodegradation result.

Nitrate removal from low carbon-to-nitrogen ratio wastewater by combining iron-based chemical reduction and autotrophic denitrification

Nitrate removal from low carbon-to-nitrogen ratio (C/N) wastewater has always been a knotty problem due to the deficiency of organics. Here, a novel iron-based chemical reduction and autotrophic denitrification (ICAD) system was developed. ICAD system could maintain average nitrate removal efficiency of 97.2% for 131 days with feeding 20.3 mg NO3–-N/L at hydraulic retention time (HRT) of 24 h. The optimal operational conditions was further explored, and results demonstrated that average nitrate removal efficiency of 85.5% and 98.4% could be achieved at HRT of 12 h and 24 h (influent 20.3 mg NO3–-N/L), while average nitrate removal efficiency could reach 96.3% at optimal HRT of 12 h (influent 10.3 mg NO3–-N/L). Hydrogenophaga, which can carry out hydrogenotrophic denitrification, showed a positive correlation with nitrate removal efficiency of the ICAD system. Low cost and simple operation make the ICAD system suitable for large-scale application.

Comparison of Performance in a Bioelectrochemical System for Simultaneous Denitrification and Vanadate (V) Removal Using Hydrogen as the Sole Electron Donor

An auto-hydrogenotrophic bioelectrochemical system (BES) was set up to investigate the performance of removing nitrate (NO3−–N) and vanadate (V(V)) simultaneously. In this BES, hydrogen is produced during electrolytic reactions and the microorganisms on cathode biofilm can use it as the electron donor to reduce NO3−–N and V(V). This experiment confirmed that the removal efficiency of nitrate and vanadate could be improved by increasing the electric current and extending the hydraulic retention time (HRT) appropriately. The optimal electric current for the reactor was 200 mA with the optimum denitrification efficiency of 94.12%, vanadate removal efficiency of 77.55%. The optimal HRT was 12 h with the optimum denitrification efficiency of 94.40% and vanadate removal efficiency of 86.71%. However, by increasing the influent concentration of V(V), the removal efficiency of NO3−–N and V(V) were both reduced. These findings may help to reveal the biogeochemical fate of V(V) and nitrate in aquifers and develop technology that can simultaneously remove them from groundwater.

Biogas production from recycled paper mill wastewater by UASB digester: Optimal and mesophilic conditions

The anaerobic digestion (AD) has become an alternative source and an attractive treatment method. Up-flow Anaerobic Sludge Blanket (UASB) digester has been designed to treat the Recycled paper mill wastewater (RPMW) in Morocco. This paper provides a research on anaerobic digestion of RPMW using UASB technology. The UASB digester was designed following the characterization of wastewater and the feed rate, with the volume of 70 liters. The UASB reactor treating the RPMW was operated for 130 days with minimal overload problems. The experiments were carried out in the mesophilic temperature (37 °C) at different organic loading rates (OLR). A daily analysis was performed to ensure the efficiency of the digester. In this study, the AD experiment was performed in continuous mode with an effluent inlet flow rate equal to 1 L/h. Using the optimal OLR value 5.18 g COD/Ld and with an effluent 5,7 g COD/L, a biogas yield of 92 N mL/g COD removed (at normal temperature and pressure) was obtained during the RPMW anaerobic treatment. The reactor was operated at an optimal hydraulic retention time (HRT) of 15.14 h with a biogas production volume of the optimal value 62.5 L/d. These results indicate that RPMW can be effectively treated in a UASB reactor with the advantage of producing biogas. We tested our system with RPMW, to see the production capacity of the UASB system, which the objective is to develop the system for the industrial scale.

Comparation of thermophilic bacteria (TB) pretreated primary and secondary waste sludge carbon sources on denitrification performance at different HRTs

In this study, thermophilic bacteria pretreated primary and secondary waste sludge hydrolysis and acidification liquid were used as denitrification carbon sources at different HRTs (hydraulic retention time). The NO3−-N removal rate of 99.3%, 99.0%, 99.9% and 99.2% was achieved at the optimal HRT of 8, 8, 4 and 6 h, respectively. Meanwhile, the utilization of COD (Chemical oxygen demand), proteins, carbohydrates, and VFAs (Volatile fatty acids) in carbon source during denitrification was also investigated. High-throughput sequencing technology showed that the microbial community changed with the different sludge carbon sources. And the dominant genus in both reactors was Thauera, which played a key role in denitrification.

A study of the treatment of high-salt chromium-containing wastewater by the photocatalysis-constructed wetland combination method.

In this study, iron ore slag as the photocatalyst was introduced into a constructed wetland simulation system. A comparative experiment of the constructed wetland method and photocatalysis-constructed wetland combination method that treats the high-salt chromium-containing wastewater was carried out. The best hydraulic retention time (HRT) of the photocatalysis-constructed wetland combination system was studied. The effects of these two methods on biochemical oxygen demand (BOD5), chemical oxygen demand (COD) removal and Cr(VI) reduction rate of the high-salt chromium-containing wastewater were analysed after 14 periods. The results showed that under the optimal HRT of 4 hours, the COD and BOD5 of the wastewater reduced by 47% and 31%, and the reduction rate of Cr(VI) was 83% separately in the constructed wetland system. The COD and BOD5 of the wastewater reduced by 83% and 42%, and the reduction rate of Cr(VI) was 96% separately in the photocatalysis-constructed wetland combination method system. At the same time, the changes in plant parameters under these two systems were studied, and the results showed that the addition of photocatalyst and hydrogen peroxide to constructed wetlands did not affect the normal indicators of plant growth. The results showed that the photocatalysis-constructed wetland combination method not only reduced the treatment time greatly, but also improved the quality of the treated wastewater significantly.

Treatment of Sugar Industry Effluent Through SBR Followed by Electrocoagulation

Sugar industry effluent (SIE) is characterized as high organic load. The aim of present work is to treat SIE in sequential batch reactor (SBR). Effect of hydraulic retention time (HRT) on COD reduction was studied at instantaneous fill condition. Maximum 67.2% COD removal was achieved at HRT of 2.33 days (d) in 10 h of treatment. At optimum HRT of 2.33 days, the fill time (tF) of the effluent was varied to treat it, in which tF of 1.5 h was evaluated to optimum for maximum of 91.66% COD removal of initial COD of 4800 mg/dm3 achieved in 10 h of treatment. The effluent treated in SBR was further followed by electrocoagulation (EC) using mild steel (MS) electrode. The initial COD of 640 mg/dm3 was reduced to 77 mg/dm3 at operating condition of current density 69.44 A/m2 (2A) and treatment time (tR) ~ 90 min. The kinetics of degradation of SIE in SBR was also evaluated.

Biogas production from palm oil mill effluent and empty fruit bunches by coupled liquid and solid-state anaerobic digestion

Biogas production of palm oil mill effluent (POME) and empty fruit bunches (EFB) was performed by coupled liquid (L-AD) and solid-state (SS-AD) anaerobic digestion processes. POME was fed to L-AD digester, while mixed of effluent from L-AD and EFB was fed to SS-AD digester. The maximum overall methane production of 60.9 m3-CH4·ton−1 waste was obtained at an optimal hydraulic retention time of 30 days and an organic loading rate of 1.66 gVS·L−1-reactor·d−1 for L-AD and 6.03 gVS·L−1-reactor·d−1 for SS-AD with L-AD effluent recycling rate of 16.7 mL·L−1-reactor·d−1. The bacterial community in the L-AD reactor was different from the SS-AD reactor, while the archaeal community was similar in both reactors. Synergistaceae, Caldicoprobacteraceae and Lachnospiraceae were increased in the SS-AD reactor. Coupling L-AD and SS-AD is able to increase energy production by 29% and 71% compared to the L-AD and SS-AD alone, respectively, with no outsource SS-AD inoculum required.

Performance evaluation of fixed bed anaerobic baffled reactor and its upgrading by integrated electrocoagulation process for municipal wastewater treatment

Anaerobic baffled reactor is efficient for wastewater treatment, while it lacks efficient nutrient removal and must be upgraded. The present study aimed to evaluate performance of fixed-bed media anaerobic baffled reactor (FABR) for municipal wastewater treatment. The performance of the integrated electrocoagulation process in the FABR (E-FABR) was also investigated. The large bench-scale five of sectional FABR reactor was assessed continually to the hydraulic retention times (HRTs) of 40, 30, and 20 hours, respectively to meet the effluent disposal standards using the HDPE-2H media in the FABR. After determining the optimum HRT, EP was integrated in 4th section of the FABR to improve the performance. At the E-FABR, the steel-steel and aluminum electrode pair (Al-Al) was evaluated at the current densities of 0.05-0.5 mA/cm2 (HRT=20 hours). The performance of FABR decreased with reduced HRT from 40 to 30 and 20 hours. At the optimum HRT (30 hours), the reactor met the TSS, COD, and BOD effluent discharge standards. The mean steady-state removal of TSS, COD, BOD5, total nitrogen, and total phosphorus was 93±0.5%, 91±0.8%, 93.4±1%, 16±1%, and 28±0.7%, respectively. The E-FABR with the steel and aluminum electrodes at the current densities of 0.3 and 0.1 mA/cm2 and HRT of 20 hours decreased the TSS, COD, BOD, SO4, and TP concentrations to the effluent discharge standard limits. Therefore, the FABR is an efficient system for municipal wastewater treatment, and E-FABR with aluminum electrodes and extremely low current density could easily treat wastewater to the effluent discharge standards.

Evaluation of an anaerobic baffled reactor for pretreating black water: Potential application in rural China

Black water is highly concentrated human waste water but represents only a minor portion of domestic sewage. A modified type of anaerobic baffled reactor (ABR) was studied to assess its potential for pretreating black water in rural China. The classification of microbial structure was also investigated to confirm its potential in application. The structure of the ABR was modified according to demand for application in practice. A hydraulic retention time (HRT) of 48 h was chosen as the optimal HRT after comparison among 24 h, 36 h, 48 h, and 72 h. Under the 48 h HRT, the ABR achieved average removal efficiencies of 94.05% of chemical oxygen demand (COD), 28.78% of total nitrogen (TN), 14.21% of ammonium nitrogen (NH4+-), and 32.54% of total phosphorus (TP) during 112 days of continuous operation. Samples from three different compartments were collected after 60-day continuous operation for bacterial and archaeal community investigation by 16S rRNA. Abundant degradation-related bacteria and methanogenic archaea were found in the ABR. The three samples had similar bacterial compositions at phylum, class, and genus levels, but the percentages of bacteria differed among the compartments. The distribution of archaea showed succession with the flow direction. In general, the ABR shows good performance under an HRT of 48 h and shows good potential for practical application.

Treatment of Balili River in Benguet, Philippines with constructed wetland planted with dominant local macrophytes

Phytoremediation using local macrophytes was explored in Balili River, Philippines. The macrophytes used were Amaranthus spinosus, Eichhornia crassipes, Eleusine indica and Pennisetum purpureum planted in pilot-scale constructed wetlands and subjected to varying hydraulic retention time (HRT) treatments. Results showed that these macrophytes have high phytoremediation performance in almost all water quality parameters. Also, HRT significantly affected the pollution reduction efficiency of the macrophytes. Significant pollution reduction was observed as early as HRT 1 day, but the optimal HRT for all the macrophytes was 3–4 days. At optimal HRT, the pollution reduction efficiency of the four macrophytes ranged from 96% to 99.9% for TSS, 87% to 95% for BOD, 85% to 99% for NO3, 85% to 96% for PO4 and 99.9% for total and fecal coliform. Also, Hg and Pb were significantly reduced. Results of TSS, DO and NO3 passed the water quality standard, while BOD and PO4 were slightly above. But total and fecal coliform, amidst the high reduction rate, was still not within the permissible level for Class A water. Among the macrophytes, P. purpureum generally have the best pollution reduction efficiency. Our study revealed comparable or even better pollution reduction efficiency of local macrophytes than commonly used ones such as Phragmites spp. and Typha spp.

Removal of Acid Orange 7 dye from wastewater using combination of ultraviolet radiation, ultrasonic method, and MgO nanoparticles

Background: Industrial dyes are toxic and carcinogenic, therefore, they should be removed from wastewater. The aim of this study was to investigate the removal of acid orange 7 Dye from wastewater using ultraviolet (UV) radiation, MgO nanoparticles, ultrasonic method alone and in combination with each other. Methods: The effects of some factors such as temperature, pH, hydraulic retention time (HRT), UV power, and concentration of MgO nanoparticles on the removal of Acid Orange 7 dye from synthetic wastewater using different methods were investigated. Also, adsorption isotherms for MgO nanoparticles and kinetics for UV radiation were investigated. Results: The optimum HRT was 55 minutes while the temperature was not effective in dye removal using the ultrasonic method. Under optimum conditions for UV irradiation method (HRT = 70 minutes, UV power = 170 mW/cm2, and temperature = 10˚C), 58% of the dye was removed. However, under optimum conditions for MgO nanoparticles method (HRT = 15 minutes, temperature = 20˚C, and ratio of MgO nanoparticles to the initial dye concentration = 67.2), 82% of the dye was removed. By combining these methods, the dye removal efficiency was significantly increased. The combination of ultrasonic method and MgO nanoparticles had no significant effect on increasing the dye removal efficiency from wastewater. It was revealed that dye removal using UV radiation can be described by the first-order kinetics. Conclusion: According to the results, UV radiation has a synergistic effect on the dye adsorption process by MgO nanoparticles. Therefore, the combination of these methods can be effective for the removal of dye from wastewater.

An influent responsive control strategy with machine learning: Q-learning based optimization method for a biological phosphorus removal system

Biological phosphorus removal (BPR) is an economical and sustainable processes for the removal of phosphorus (P) from wastewater, achieved by recirculating activated sludge through anaerobic and aerobic (An/Ae) processes. However, few studies have systematically analyzed the optimal hydraulic retention times (HRTs) in anaerobic and aerobic reactions, or whether these are the most appropriate control strategies. In this study, a novel optimization methodology using an improved Q-learning (QL) algorithm was developed, to optimize An/Ae HRTs in a BPR system. A framework for QL-based BPR control strategies was established and the improved Q function, Qt+1(st,st+1)=Qt(st,st+1)+k·[R(st,st+1)+γ·maxatQt(st,st+1)−Qt(st,st+1)] was derived. Based on the improved Q function and the state transition matrices obtained under different HRT step-lengths, the optimum combinations of HRTs in An/Ae processes in any BPR system could be obtained, in terms of the ordered pair combinations of the <current state-transition state>. Model verification was performed by applying six different influent chemical oxygen demand (COD) concentrations, varying from 150 to 600 mg L−1 and influent P concentrations, varying from 12 to 30 mg L−1. Superior and stable effluent qualities were observed with the optimal control strategies. This indicates that the proposed novel QL-based BPR model performed properly and the derived Q functions successfully realized real-time modelling, with stable optimal control strategies under fluctuant influent loads during wastewater treatment processes.

Co-digestion of cassava starch wastewater with buffalo dung for bio-hydrogen production

Batch and continuous modes for bio-hydrogen production by co-digesting cassava starch wastewater with buffalo dung were investigated. Response surface methodology with central composite design was used to optimize the bio-hydrogen production conditions. A hydrogen production potential of 1787 mL H2/L was achieved under optimal conditions of 2.84 g/L of NaHCO3, an initial pH of 6.77 and a total chemical oxygen demand (tCOD)/total nitrogen ratio of 42.36. A continuous stirred tank reactor was operated under the optimum conditions from batch mode to investigate the effects of hydraulic retention time (HRT) of 72, 60 and 48 h on hydrogen production. The highest hydrogen content, hydrogen production rate and hydrogen yield of 33%, 839 mL H2/L.d and 16.90 mL H2/g-CODadded, respectively, were achieved at a HRT of 60 h. The predominant hydrogen producer under the optimal conditions in batch mode was Clostridium sp. while Clostridium sp., Megasphaera sp. and Chloroflexi sp. were observed in the continuous hydrogen production mode at an optimal HRT.

Biohydrogen production in pilot-scale fermenter: Effects of hydraulic retention time and substrate concentration

Systematic investigation of the effects of hydraulic retention time and substrate concentration on biohydrogen production rates in pilot-scale fermenter is of great academic and practical interests. The present study applied a 3 m3 pilot-scale bioreactor that composed of three sequential 1 m3 chambers (#1-#3) to investigate the effects of hydraulic retention time and substrate concentration on biohydrogen production rates from glucose. The 48 h hydraulic retention time resulted in poor mixing of the medium; chamber #1, which received the feed substrate, converted too much glucose, and little glucose was left to be utilized in the following chambers. However, a 12 h hydraulic retention time allowed insufficient volatile fatty acids to be produced, so a reductive environment for biohydrogen production was difficult to establish. At the optimal hydraulic retention time, 24 h for the present fermenter, sufficient mixedness of the medium and fermentation times for all chambers maximized the biohydrogen production rates. Biohydrogen production rates were increased as the substrate concentration was increased from 10 to 30 g/L, peaked at 100.16 mol/m3-d, and then decreased with the increase in substrate concentration. Unique in the literature, the reported data reveal the effects of substrate concentration on biohydrogen production rates in pilot-scale fermenter, guiding to the design and development of the pilot-scale bioreactors with high hydrogen yields that could help to improve the industrialization development of biohydrogen production.

Nitrogen Removal Performance of a Sulfur/Pyrite Autotrophic Denitrification System

In order to search for an economical, rapid, and highly efficient nitrogen removal process for sewage, a sulfur/pyrite packed column reactor was fed with low C/N municipal sewage. The effects of temperature, the sulfur-to-pyrite volume ratio, and hydraulic retention time (HRT) on nitrogen removal were studied. The results showed that with an influent total nitrogen (TN) of 40 mg·L-1, the optimal HRT of the No.1 reactor was 2.5 h, and the removal rate and effluent concentration of TN were stable at 72.2% and 10.55 mg·L-1, respectively. The optimal HRT of the No.2 reactor was 3.5 h, and the removal rate and effluent concentration of TN were stable at 67.8% and 12.90 mg·L-1, respectively. The optimal HRT of the No.3 reactor was 3.5 h, and the removal rate and effluent concentration of TN were stable at 60.6% and 15.00 mg·L-1, respectively. The sulfur/pyrite autotrophic denitrification system starts faster than the pyrite autotrophic denitrification system. Its nitrogen removal rate decreased with decreasing sulfur-to-pyrite volume ratio. The nitrogen removal performance of the system is not sensitive to temperature, and the denitrification performance is better than that of the system with pyrite alone as the sulfur source. The main functional bacteria in the system are Sulfurimonas and Thiobacillus, and the proportion of the sum of these two bacteria in the three reactors decreased from No.1 to No.3.

Synergistic 1,4-dioxane removal by non-thermal plasma followed by biodegradation

In this work a water film non-thermal plasma reactor is combined with an aerobic biological reactor to treat water contaminated by 1,4-dioxane. The plasma reactor converted 1,4-dioxane to organic products including ethylene glycol, ethylene glycol monoformate, ethylene glycol diformate, 1,4-dioxan-2-one, 1,4-dioxan-2-ol, and formic, oxalic, glycolic, and methoxyacetic acids. The detection of these organic products led to a proposed novel 1,4-dioxane degradation pathway. The plasma reactor primarily utilized OH radicals formed directly from water to degrade 1,4-dioxane at an energy efficiency comparable to, but with a reaction rate over three orders of magnitude higher than that in other advanced oxidation processes (AOPs), which might be due to the significant local OH radical production. The concentration and composition of the organic products exiting the plasma reactor varied with hydraulic retention time (HRT) and affected the following biological treatment time. At the optimum HRT for the plasma reactor (i.e., 1 s), ∼25% of 1,4-dioxane was mineralized to CO2, and ∼75% was converted to organic products, which were further degraded in the following biological reactor.

Impact of hydraulic retention time and current on the microbial community and denitrification genes in a continuous‐flow biofilm electrode reactor

AbstractBACKGROUNDA biofilm‐electrode reactor (BER) was developed on the basis of hydrogenotrophic denitrification. The BER can be strengthened by adding organic matter, and the nitrate removal will be enhanced by a combination of heterotrophic and autotrophic denitrification. Denitrification in a biological system can be affected by operating parameters, and the microbial community and functional genes can be changed at the same time. In this study, the effect of hydraulic retention time (HRT) and current on the denitrification of a low chemical oxygen demand to nitrogen ratio (COD/N), saline wastewater in a continuous‐flow BER was evaluated and compared to a conventional biofilm reactor (BR).RESULTSThe highest extent of nitrate removal was obtained at the optimum HRT (8 h) and current (10 mA). Low levels of ammonia (0.5–4 mg L−1), produced through dissimilatory nitrate reduction to ammonia (DNRA), were observed. Quantitative real‐time polymerase chain reaction analysis revealed that the proportion of nirS‐type denitrifiers (3.75–8.30%) exceeded nirK‐type denitrifiers (0.24–0.90%) in both BR and BER. The genera of T78, Paracoccus and Azoarcus were identified as the dominant denitrifying bacteria in the BER. The cooperative activity of nitrate, nitrite and nitrous oxide reductase is necessary to reduce nitrate to dinitrogen in the denitrification process. The highest ratio of nosZ/nir genes in the bacterial community was 0.25 when the applied current was 10 mA.CONCLUSIONCompared to other denitrification reactors, the BER is more effective to treat low‐COD/N, saline wastewater with short HRT and low current. © 2018 Society of Chemical Industry

Bioenergy from wastewater resources: Nutrient removal, productivity and settleability of indigenous algal-bacteria polyculture, and effect of biomass composition variability on methane production kinetics and anaerobic digestion energy balance

Algal-bacteria high-rate ponds represent an energy-efficient wastewater treatment approach and a source for affordable and sustainable biomass feedstock for production of renewable energy through anaerobic digestion (AD). However, there is still a need for more data on wastewater treatment efficiency, biomass productivity and settleability from outdoor treatment facilities, as well as on impact of variability in biomass composition and digestibility on methane yield and energy output. Hydraulic retention time (HRT) and wastewater quality fed into 30 m2 raceway ponds had a major effect on algal-bacteria polyculture productivity, settleability, phylogenetic and biochemical compositions, digestibility and methane yield. While Micractinium, Scenedesmus, Chlorella, and pennate diatoms were always among the key species observed, the gross productivity and 2-hour settleability during summer cultivation varied in the first-stage ponds treating primary wastewater from 29 ± 5 to 54 ± 12 gAFDW/m2/d and from 88 ± 8 to 94 ± 4% for HRT of 3 and 2 days, respectively. For these conditions, the effluent had csBOD of 3.4 or 3.3 mg/L and Ntotal (mostly NO3−-N) of 9.2 or 8.2 mg/L, respectively. The second-stage algal ponds (HRT 3 days) showed lower productivity of 16 ± 6 gAFDW/m2/d, settleability of 84 ± 11%, and effluent csBOD 3.7 mg/L and Ntotal 0.8 mg/L. Biomass composition from different ponds was 34–38% protein, 18–28% total lipids and 6–14% FAME. The methane yield varied about 30% with largest value of 0.34 ± 0.01 L/gVS and showed a positive correlation with biomass lipid content (R2 = 0.93). First-order and pseudo-parallel first-order rate kinetic models exhibited a better fit for methane production (most R2 > 0.993) than the modified Gompertz model. The variation in biomass composition led to significant differences in energy output (varied by about 60%), Net Energy Ratios (ranged from 1.6 to 2.2) and Net Energy Efficiency (from 60% to 70%) when projecting the energy balance for a large-scale continuous AD process with an optimal HRT of 20–30 days.

Denitrification process of deep bed denitrification filter for secondary effluent from urban sewage treatment plant

In recent years, the sewage discharge standards are getting stricter, and advanced wastewater treatment is more important. Therefore, further advanced treatment of the effluent from the wastewater treatment plant has become a research hotspot. In this study, deep bed denitrification filter (DBDF) was used to treat secondary effluent from urban sewage treatment plants. The effects of different carbon and nitrogen ratios (C/N) and hydraulic retention time (HRT) on the nitrogen removal efficiency of the system were investigated. The results showed that the optimum C/N of the reactor was 5, and the optimum HRT was 0.5h. After running for 15 days under the optimal conditions, the results showed that DBDF ran stably, and the denitrification effect was good. The average effluent concentrations of COD and TN were 16.4 and 6.9mg/L, and the average removal rates were 77.0% and 57.7% respectively.