Hydraulic Retention Time Values Research Articles

Improving organic and nutrient removal efficiencies in seafood processing wastewater using anaerobic membrane bioreactor (AnMBR) integrates with anoxic/oxic (AO) processes

Wastewater from seafood processing is a significant source of pollution, containing many harmful organic and inorganic compounds such as proteins, lipids, carbohydrates, nitrogen and phosphorus. This study investigated the enhancement of organic and nutrient removal efficiencies in seafood processing wastewater by integrating an Anaerobic Membrane Bioreactor (AnMBR) with an anoxic/oxic (AO) processes. A pilot-scale system was constructed with a capacity of 0.5 m3/day directly at the factory operated continuously, featuring an AnMBR process with a 24-hour hydraulic retention time (HRT) and an AO process with HRT values and internal recycle changes. The AnMBR system exhibited consistent and high-performance biochemical oxygen demand (COD) elimination, approximately 80 ± 5 %. However, this system demonstrated low-efficiency removal of total nitrogen (TN) at about 20 ± 5 %, and total phosphorus (TP) 15 ± 5 %, under organic loading rates (OLR) of 0.6 to 1.3 kg-COD/(L·d). The AO process was then continually employed to improve the treatment efficacy (at HRT, 5 h in the anoxic phase, and 8.3 h in the oxic phase, at a recycling rate of 300 %) resulting in the final post-treatment concentrations of COD 27–41 mg/L (removal 98.3 ± 0.3 %), TN 12–25 mg/L (90 ± 2 %), and TP 18 ± 2 mg/L (35 ± 5 %). The performance of the integrated AnMBR-AO system met the established Vietnamese discharge standards for seafood processing wastewater, as outlined in QCVN 11-MT: 2015/BTNMT.

Performance evaluation of MBR-RO technology for domestic wastewater treatment

Abstract This study was carried out to evaluate the treatment efficiency of domestic wastewater using Membrane Bioreactor combined Reverse Osmosis (MBR-RO) technology. The optimal hydraulic retention time (HRT) of the MBR was studied at various HRT value of 1h, 4h, and 8h. The MBR-RO reactor was then operated at optimal HRT for domestic wastewater treatment. The research result showed that the MBR has an optimal HRT of 4h. The removal efficiency of TSS, COD, BOD, TN, and TP in the MBR was 100%, 99.57%, 100%, 73.33%, and 94.41%, respectively. The MBR-RO system can completely remove organic and nutrient pollutants from wastewater with the removal efficiency was 100% for TSS, COD, BOD, TN, and TP. Consequently, the MBR-RO effluent meets the Vietnam regulation standard of QCVN 08:2015/BTNMT and QCVN 01-1:2018/BYT. Research results show the potential of applying MBR-RO membrane technology for domestic reuse purposes.

Retention time and organic loading rate as anaerobic co-digestion key-factors for better digestate valorization practices: C and N dynamics in soils

The growing use of anaerobic co-digestion (AcoD) in processing organic waste has led to a significant digestate production. To effectively recycle digestate back into soils, it is crucial to understand how operational variables in the AcoD process influence the conversion of organic matter (OM). To address this, a combination of biochemical fractionation and various soil incubation tests were employed to assess the stability of OM in digestates generated from anaerobic continuous reactors fed with a food waste-hay mixture and operating at different hydraulic retention times (HRT) and organic loading rates (OLR). This study revealed that digester performance and operating parameters impacted carbon dynamics in soils. A decrease in the carbon mineralization in soils when increasing the HRT was reported (48 ± 4 % for 70 days compared to 59 ± 1 % for 42 days). Specific HRT and OLR values were found to be linked to carbon accessibility and complexity, confirming that longer HRT lead to higher OM removal and increased complexity in soluble OM, despite minor discrepancies in relative carbon distribution. Furthermore, comparable rates of nitrogen mineralization in soils were observed for all digestates, consistent with the accessibility of nitrogen from the particulate OM. Nevertheless, AcoD converted substrates with the potential to immobilize nitrogen in soils into fast-acting fertilizers. In summary, this study underscores the importance of controlling the AcoD performances to evaluate the suitability of digestates for sustainable agricultural practices.

MIB-derived odor management based upon hydraulic regulation in small drinking water reservoirs: Principle and application

The musty odorant (2-methylisoborneol, MIB) is prevalent in source water reservoirs and has become one of the major challenges for drinking water quality. This study proposes an approach to control the growth of MIB-producing cyanobacteria in a small reservoir based on hydraulic regulation, according to the results of long-term field investigations, laboratory culture experiments, model construction, and field application. Field investigations found that longer hydraulic retention time (HRT) is a factor that triggers MIB episodes. The culture study revealed that the maximum cell density, growth rate of MIB-producing Planktothricoides raciborskii, and MIB concentration are determined by the HRT (R2= 0.94, p-value < 0.001) and can be minimized by decreasing the HRT to less than 10 d. On this basis, an HRT regulation model was constructed and validated by field investigation, and critical HRT values were evaluated for 14 cyanobacteria genera. By decreasing the HRT to 5.4 ± 0.8 d, which is lower than the critical value of 7.5 ∼ 15.0 d, an MIB episode was successfully terminated in ZXD Reservoir in 2021. The results suggest that the proposed principle can provide a scientific basis for HRT regulation, which has been proved to be effective and feasible. This approach avoids negative impacts on water quality, does not require extra investment in engineering infrastructure, and in some cases may be applied readily by changing existing operational procedures. Therefore, HRT-based regulation is a promising strategy targeting MIB control and possibly for other cyanobacterial-derived water quality problems in small reservoirs.

Impact of extended versus typical rapid mixing HRTs on continuous-flow coagulation-ultrafiltration

Although bench-scale coagulation-ultrafiltration (UF) studies are typically conducted using batch systems, continuous-flow systems allow operational parameters to be more readily evaluated and optimized over consecutive permeation cycles. When simulating coagulation-UF at bench-scale using continuous-flow systems, relevant reactor volumes require flowrates ≥1 L/min in order to achieve hydraulic retention times (HRTs) typical of full-scale rapid mixing (30 s to several minutes). In the present study, HRTs of 2 and 20 min were evaluated to determine their impact on particle properties (size, structure, and concentration) as well as UF performance (fouling resistance, reduction of natural organic matter) over a range of alum dosages. While not practical at full-scale, a 20 min HRT has been previously applied at bench-scale to reduce the overall volume of water required to conduct continuous-flow coagulation-UF studies. However, potential impacts on steady-state particle properties and subsequent UF performance not been clearly elucidated. Results from this study suggest that increasing HRT significantly increases steady-state particle size and concentration, as well as reduces total/hydraulically irreversible UF fouling resistance and improves hydraulic cleaning efficiency. Despite reduced fouling when considering a longer HRT, significant differences in particle properties and UF performance suggest that HRT values equivalent to those typically applied during full-scale rapid mixing (30 s to several minutes) must be considered in order to produce results relevant to full-scale.

Antibiotic removal from swine farming wastewater by anaerobic membrane bioreactor: Role of hydraulic retention time

This study investigated the impact of hydraulic retention time (HRT) on the removal of veterinary antibiotics by an anaerobic membrane bioreactor (AnMBR) for swine wastewater treatment. Ten commonly used antibiotics in the group of tetracyclines, fluoroquinolones, and sulfonamides were evaluated. Results show that a wide variation from 21 to 99% was observed for antibiotic removal by AnMBR regardless of the applied HRT. The methane yield increased from 0.22 L/g COD to 0.28 L/g COD as the operational HRT was prolonged from 24 to 48 h for AnMBR. Doubling the HRT value enhanced removal of most antibiotics and methane yield by 2–30% and 22–47%, respectively. The enhanced antibiotic removal in response to HRT prolongation could be positively correlated to the enrichment of the genus unidentified_Synergistaceae. Moreover, prolonging HRT increased the relative abundance of the genera unidentified_Synergistaceae, Geobacter and Methanobrevibacter, which could strengthen hydrogenotrophic methanogenesis to enhance methane yield. In addition, HRT increase reduced the ratio of protein to polysaccharide in both extracellular polymeric substances and soluble microbial products, thereby, alleviating membrane fouling in AnMBR operation.

Carboxylic acids production via anaerobic fermentation: Microbial communities’ responses to stepwise and direct hydraulic retention time decrease

Carboxylic acids, traditionally produced from fossil fuels, might be generated from renewable biomass resources via anaerobic fermentation. Considering that the microbial activity of this bioprocess is ruled by the imposed hydraulic retention time (HRT), this investigation explored the relationship between process stability and microbial community. Stepwise and direct HRT reduction strategies were assessed in terms of waste bioconversion into volatile fatty acids (VFAs). Microbial community dynamics revealed a microbial specialization along the HRT decrease. The direct implementation of low HRT resulted in drastic microbial fluctuations, leading to process failure at HRT below 6 days. Stepwise strategy for HRT reduction favored microbial adaptation, supporting maximum bioconversions efficiencies (32 % VFACOD/tCODin) at low HRT values (HRT 4 days). Microbial similarity analysis revealed Clostridiales, Lactobacillales and Bacteroidales orders as keystone microorganisms involved in VFAs production, being responsible for protein degradation and propionic acid accumulation.

Impact of turbidity, hydraulic retention time, and polarity reversal upon iron electrode based electrocoagulation pre-treatment of coal seam gas associated water

The applicability of iron (steel) electrodes in a continuous electrocoagulation (EC) process to treat coal seam gas (CSG) associated water comprising of a high level of turbidity (421 NTU) was studied. Key objectives were to understand the influence of turbidity upon water quality when hydraulic retention time (HRT) and polarity reversal time (PRT) were tested using a bench top EC unit. Extension of HRT promoted removal of dissolved alkaline earth ions (Ca 23 to 45 %; Mg 60 to 97 %; Ba 25 to 54 %; Sr 10 to 19 %), silicates (90 to 93 %) and boron (8 to 12.7 %); whereas turbidity was optimally reduced at a HRT value of 30 s (98.5 %). Turbidity particularly promoted magnesium removal which may be due to destabilization of the clay suspension. However, clay particles also inhibited the rate of floc settling. The greater performance of EC with increasing HRT was achieved at a cost of increased consumption of electrodes and electricity. PRT reduced power consumption with an optimal value being at least 5 min (4.12 to 3.88 kWh/kL for PRT values of 1 and 5 min, respectively). Removal rates of dissolved species were not greatly influenced by PRT. Surface passivation at low PRT values produced higher amounts of hydrogen gas which caused the flocs to float. In summary, HRT, PRT, turbidity level and solution composition were critical parameters in relation to the potential use of EC in the CSG industry.

Design of the Reactor and the Clarifier of an Activated Sludge Water Resource Recovery Facility, AS WRRF

Metcalf & Eddy´s formula that gives the mixed liquor volatile suspended solids, MLVSS= Xv, produced in the aeration tank, from hereon called Reactor, will be used giving it the parameters for AS WRRFs shown in Table 10-5 of its 3rd Edition placing values of hydraulic retention time, HRT, in the first column and values of solids retention time, SRT, in the first row. Many solutions are found that solve the formula. Some will be studied, using the flux graph, to check if they comply with other requirements as moderate volume, V, of Reactor, small surface, S, of Clarifier, ample range of return flow percentages, R, and admissible relation F/M. A solution will then be chosen.

Optimization of a novel single air-lift sequencing bioreactor for raw piggery wastewater treatment: Nutrients removal and microbial community structure analysis

In this study, a sequencing batch and intermittent air-lift bioreactor (SBIAB) was evaluated under the three independent variables to treat raw piggery wastewater. The effects of hydraulic retention time (HRT), air flow rate and sludge retention time (SRT) on the nutrients removal of SBIAB were researched. The optimum values of HRT, air flow rate and SRT were 8 d, 2 l/min and 20 d, respectively. Meanwhile, the removal rates of chemical oxygen demand (COD), NH4+-N, total nitrogen (TN) and total phosphorus (TP) were up to 89.5%, 93.5%, 61.1% and 57.3%, respectively. Generally, the nutrients removal performance could be enhanced with increasing HRT from 6 to 10 d, while it was inhibited at air flow rate of 3 l/min. Higher air flow rate caused the alkaline pH and high free ammonia concentration, which imposed restrictions on the process of wastewater treatment. In the SBIAB, a coupling of aerobic/anoxic/anaerobic zone was formed according to the changes of oxidation-reduction potential (ORP) values at the optimum condition. Microbial community structure analysis indicated that the functional microbes including Brachymonas, Prokaryote, Giesbergeria, Comamonadaceae bacterium, Clostridiales bacterium, Comamonas, Tissierella, Aequorivita were enriched in the SBIAB, which played a significant role in the removal of complex organics and nitrogen.

Removal of personal care products (PCPs) from greywater using a submerged membrane bioreactor (SMBR): The effect of hydraulic retention time

The rising trend of depletion in global water supplies and the consistent accumulation of emerging environmental contaminants in water, soil and plant have become an international concern during the past decade. In recent years, the removal of personal care products (PCPs) from greywater has inspired a great attention for facile water recycling. In this study, the performance of a specially designed submerged membrane bioreactor (SMBR) system toward high-efficiency degradation of PCPs released through household greywater was investigated. The influent PCP-rich greywater was prepared by mixing commercial PCPs and the SMBR operated under different hydraulic retention time (HRT) values for 150 days of continuous operation. The results revealed that HRT has a striking influence on the treatment performance of the SMBR for PCP contaminants while the SMBR displayed a superior degradation capability for all categories of PCP contaminants (including antimicrobial agent, preservative, fragrance and UV Filter) at the effluent stream. Triclosan, methylparaben and propylparaben as the contaminants with the highest concentration at prepared PCP-rich greywater were removed up to 98.20%, 99.96% and 99.97%, respectively and other ones had more than 64% removal efficiency at HRT of 16 h. The chemical oxygen demand (COD) and biological oxygen demand (BOD) at the optimum HRT value were negligible.

Simultaneous denitrification, phosphorus recovery and low sulfate production in a recirculated pyrite-packed biofilter (RPPB)

The simultaneous removal of nitrate (15 mg N-NO3- L−1) and phosphate (12 mg P-PO43- L−1) from nutrient-polluted synthetic water was investigated in a recirculated pyrite-packed biofilter (RPPB) under hydraulic retention time (HRT) ranging from 2 to 11 h. HRT values ≥ 8 h resulted in nitrate and phosphate average removal efficiency (RE) higher than 90% and 70%, respectively. Decrease of HRT to 2 h significantly reduced the RE of both nitrogen and phosphorus. The RPPB showed high resiliency as reactor performance recovered immediately after HRT increase to 5 h. Solid-phase characterization of pyrite granules and backwashing material collected from the RPPB at the end of the study revealed that iron-phosphate, -hydroxide and -sulfate precipitated in the bioreactor. Thermodynamic modeling predicted the formation of S0 during the study. Residence time distribution tests showed semi-complete mixing hydrodynamic flow conditions in the RPPB. The RPPB can be considered an elegant and low-cost technology coupling biological nitrogen removal to the recovery of phosphorus, iron and sulfur via chemical precipitation.

Impacts of hydraulic retention time on granule behaviour and reactor activity during hydrocarbon degradation in aerobic granular reactors (AGRs) with phytotoxicity analysis

The paper is about impacts of hydraulic retention time (HRT) on granule characteristics, reactor activity, hydrocarbon removal efficiency and removal mechanism while treating emulsified diesel wastewater in aerobic granular reactors (AGRs). AGR with shortest HRT (12 h) achieved maximum 4.72 ± 0.05 mm granule size and extracellular polymeric substances (EPS) of 400.31 ± 0.01 mg/g volatile suspended solids (VSS) with 68.85 ± 0.06% of hydrocarbon removal. Short HRT (12 h) provided maximum biomass concentration (6.38 ± 0.05 g/L) to achieve maximum biomass activity of 8.33 ± 0.21 mg COD/mg VSS.day among the AGRs. But longest HRT (48 h) played major role providing longer reaction time for 90.31 ± 0.26% hydrocarbon removal. Degradation of short and long chain alkanes (C6–C7, C9–C10, C11–C13, C15–C18, C27) were observed in the AGRs which further produced fatty acids as metabolites. In steady state COD removal rate varied between 71- 90% which was completely depended on HRT values and hydrocarbon removal efficiency of the reactors. Nitrogen balance suggested that maximum nitrogen was utilized in biomass growth and about 2–20% nitrification occurred in the AGRs. About 24–48 h HRT with 0.125–0.25 kg/m3.day hydrocarbon loadings providing below 77 mg/L effluent hydrocarbon was recommended for successful AGR treatment to avoid phytotoxicity after disposal.

Self-regenerating tubing bioreactor for removal of toxic substrates: Operational strategies in response to severe dynamic loading conditions

A tubing TPPB (Two-Phase Partitioning Bioreactor) was operated with the objective of verifying the effective treatment of a phenolic synthetic wastewater with simultaneous polymeric tubing bioregeneration by introducing tubing effluent recycle and modifications to the Hydraulic Retention Time (HRT). 2,4-dichlorophenol (DCP) was employed as the target substrate and the bioreactor was operated for a 3 month period under severe loading conditions (from 77 to 384 mg/L d) with HRT in the tubing in the range of 2–4 h. Tubing effluent recycle (recycle flow rate/influent flow rate ratio = 0.3) was applied when a loss of performance was detected arising from the increased load. For HRT values of 3 and 4 h, almost complete DCP removal was achieved after a few days (1–5) of operation while for the 2 h HRT (i.e. in the most severe loading condition) the DCP removal was ≥97%. A beneficial effect on the process performance arising from recycle application was evident for all the operating conditions investigated, and was confirmed by statistical analysis. Essentially complete polymer bioregeneration was achieved when the bioreactor was operated at the lowest HRT (i.e. 2 h), combined with the application of tubing effluent recycle. The results of this study highlighted several advantages of the tubing TPPB configuration in a comparative analysis of different regeneration options, including the possibility of operating continuously with simultaneous bioregeneration and without the need for additional units or operational steps and extra-energy consumption.

Biohydrogen production from organic solid waste in a sequencing batch reactor: An optimization of the hydraulic and solids retention time

Hydrogen production from organic solids waste was evaluated using a sequencing batch reactor (SBR) under mesophilic conditions, to investigate the effect of the hydraulic retention time (HRT) and solids retention time (SRT) on hydrogen production. The examined HRT and SRT values were from 4.6 to 27 h and 17–102 h, respectively. The results showed high hydrogen production rates (1.86 LH2/L·d) and a yield of 127.26 mLH2/gCODremoved for an SRT of 60 h and an HRT of 16 h. The highest chemical oxygen demand (COD) removal (38.6 ± 6.9%) was also obtained under those conditions. The highest substrate hydrolysis percentage (73.0 ± 11.4%) was obtained at an HRT of 16 h and an SRT of 102 h. A short SRT of 20 h affected hydrogen production, which decreased up to 90%. With an SRT of 20 h and an HRT of 16 h, acetic acid-like fatty acids were mainly obtained. In experiments with a long SRT (60 h), the obtained fatty acid was butyrate. The conversion efficiencies for converting particulate material into fatty acids were 51–47% using a long SRT; a short HRT resulted in percentages of 37–40%. A 3D surface analysis was performed using the maximum hydrogen yield conditions as the central point, showing that the optimal hydrogen production can be obtained with an HRT of 16 h and an SRT of 55 h. Microbial analysis showed the predominance of the Olsenella genus at an HRT< 8 h and the presence of Clostridium at an HRT of 16 h. The HRT is the main parameter leading the community composition in the process.

The share of electrochemical reduction, hydrogenotrophic and heterotrophic denitrification in nitrogen removal in rotating electrobiological contactor (REBC) treating wastewater from soilless cultivation systems

There is a growing global environmental problem of agricultural wastewater from soilless plant cultivation systems. In most countries dominate open fertilization systems, in which excess of nutrient solution is discharged in an uncontrolled way into the ground inside greenhouses or adjacent areas. Wastewater from such systems is characterized by a very high concentration of nitrogen and phosphorus compounds and their discharge into the environment causes significant pollution of the water and soil environment.The goal of the research was to determine the contribution of electrochemical reduction of nitrogen, hydrogenotrophic and heterotrophic denitrification in the process of nitrogen removal in a rotating electrobiological contactor (REBC) depending on hydraulic retention time (HRT) and electric current density (J). Synthetic sewage with characteristics corresponding to wastewater from soilless cultivation of tomatoes was the subject of the research. The first part of the experiment included determination of the effect of HRT on the effectiveness of bio-processes of nutrients removal in a rotating biological contactor (RBC). The second concerned the effect of HRT and J on the effectiveness of nutrients removal in a rotating electrochemical contactor (RECC), while the third part - the effect of HRT and J on the effectiveness of nutrients removal in REBC.RBC was characterized by low efficiency of denitrification (6.2 to 9.2%). The effectiveness of nitrogen removal in RECC was determined by both electric current density and hydraulic retention time. The highest efficiency was 53.4%.REBC nitrogen removal effectiveness was higher than in RBC and in RECC. The nitrogen removal efficiency increased along with increasing values of HRT, reaching the maximum value of 68.6% for J=10.0A/m2 and HRT=24h. The contribution of hydrogenotrophic denitrification in total nitrogen removal increased with the increase of electric current density.

Upgrading Conventional Activated Sludge System Using Bio-media: A Case Study of Zenin Wastewater Treatment Plant, Egypt

This study investigated the ability to upgrade the biological treatment system in Zenin wastewater treatment plant, in Egypt. This investigation was conducted through the comparison of three different biological treatment systems: activated sludge process (AS), moving bed biofilm reactor (MBBR), and integrated fixed film activated sludge system (IFAS). Three pilot systems were established at Zenin wastewater treatment plant, to simulate AS, MBBR, and IFAS systems, to show the effect of various parameters on the removal efficiencies of biochemical oxygen demand (BOD 5 ), total suspended solids (TSS), and ammonium-nitrogen (NH 4 -N). Different values of hydraulic retention time, different amounts of returned sludge, and concentration of dissolved oxygen, were examined. The maximum removal efficiencies of BOD 5 , TSS, and NH 4 -N were 50%, 81.9%, and 82% in activated sludge system, respectively; 80%, 81.8%, and 99.3% in MBBR system, respectively; and 62.3%, 86.2%, and 76% in IFAS system, respectively. Keywords: Attached growth; Hybrid growth; Sludge; Suspended growth; Wastewater DOI : 10.7176/CER/11-1-05

Process performance and multi-kinetic modeling of a membrane bioreactor treating actual oil refinery wastewater

The performance of a membrane bioreactor treating oily wastewater generated by a petroleum refinery was investigated at mixed liquor suspended solids concentrations of 6.5 and 8.5 g/l with hydraulic retention times ranging from 12 to 24 h. An evolutionary polynomial regression technique and multi-kinetic models consisting of the first-order, Grau second-order, and modified Stover-Kincannon were applied for predicting the performance of the bioreactor. The results showed that a maximum chemical oxygen demand reduction of 97% is achievable at the mixed liquor suspended solids of 8.5 g/l and hydraulic retention time of 24 h. The results also revealed positive influence of higher mixed liquor suspended solids and hydraulic retention time values on the bioreactor performance. In addition, the high accuracy of the evolutionary polynomial regression evidenced its capability in investigating the membrane bioreactor. Based on the analysis performed by the resulted model from the evolutionary polynomial regression, the optimum operating conditions (hydraulic retention time of 21 h; mixed liquor suspended solids of 8.2 g/l) were recommended. According to the kinetic evaluation, the Grau second-order and modified Stover-Kincannon kinetics seemed to be the best approach in describing the chemical oxygen demand reduction in the membrane bioreactor.

Influence of nalidixic acid on tandem heterotrophic-autotrophic kinetics in a “NIPHO” activated sludge reactor

This work analyzes the effect of nalidixic acid (NAL) on the kinetics of the heterotrophic and autotrophic biomass growth within a “NIPHO” activated sludge reactor treating municipal wastewater. Thus, the effect of this chemical in the degradation rates of carbon and nitrogen sources and net biomass growth rate is evaluated. Activated sludge samples were taken at three different operation conditions, changing the values of hydraulic retention time (2.8–3.8 h), biomass concentration (1400–1700 mgVSS L−1), temperature (12.6–14.8 °C), and sludge retention time (11.0–12.6 day). A respirometric method was applied to model the kinetic performance of heterotrophic and autotrophic biomass in absence and presence of NAL, and a multivariable statistical analysis was carried out to characterize the influence of the operation variables on the kinetic response of the system, which was finally optimized. The results showed that there was no inhibitory effect of NAL on heterotrophic biomass, with an increase of net heterotrophic biomass growth rate from 1.70 to 6.73 mgVSS L−1 h−1 at the most favorable period. By contrast, the autotrophic biomass was negatively affected by NAL, reducing the value of net autotrophic biomass growth rate from 25.37 to 10.29 mgVSS L−1 h−1 at the best operation conditions. In general, biomass concentration and temperature had the highest influence on the degradation rate of carbon and nitrogen sources, whereas hydraulic retention time and sludge retention time were the most influential on net heterotrophic and autotrophic biomass growth rates.

The treatment of Slaughterhouses wastewater by An Up Flow - Anaerobic Sludge Blanket (UASB) reactor.

Slaughterhouse wastewater is heavily polluted. It contains a high concentration of oil and grease, phosphorus, nitrogen, organic matter and suspended solids. The objective of the research is study the ability of slaughterhouses wastewater treatment by a UASB reactor and define the best hydraulic retention time (HRT). This research focuses on the treatment of slaughterhouse wastewater in Up Flow Anaerobic Sludge Blanket (UASB) reactor In these reactors, the polluted wastewater rises slowly which allows it to form a suspended sludge blanket. Granules of sludge gather on the surface and anaerobic bacteria is activated which feeds on the organic matter which exists in the liquid. The research includes a study of the effect of hydraulic retention time (HRT) on the efficiency of treatment in UASB reactors at a constant temperature of about 30±1°C. The experiments have illustrated that it is possible to achieve excellent removal efficiency for high concentrations of COD when the temperature of the wastewater is fixed at 30±1 °C. The removal efficiency fit with hydraulic retention times (HRTs) in UASB reactor, for the following values of HRTs:(6,12,18,24,30,36) hours, the removal efficiencies of COD were:(35.78%,48.93%,56.15%,71.3% ,76.33%,83.37%) respectively.