Aeration Period Research Articles

Nitrogen Removal in Household Wastewater Treatment Using an Intermittently Aerated Membrane Bioreactor

Membrane bioreactor using a submerged hollow fiber membrane was applied in laboratory scale conditions to treat household wastewater including toilet-flushing water. The bioreactor was aerated intermittently to alternate anoxic/oxic conditions while membrane filtration occurred during the aeration period to take advantage of the air bubbles for fouling control. After being operated for about 150 days, the initial flux and suction pressure were maintained almost constant at 0.01m hr−1 and 4-6 kPa, respectively, indicating fouling control by air bubbling was very effective. With 10-15 hour hydraulic retention time (HRT), and a very long solid retention time (SRT), 97% of Total chemical oxygen demand (TCOD) and 100% suspended solids (SS) could be removed. On average, removal efficiencies for total nitrogen (TN) and total phosphorus (TP) were 83% and 55% respectively. Ammonia and coliform bacteria were completely removed. Due to the long SRT and sufficient oxygen supply, fast and complete nitrification was accomplished regardless of operational mode, and denitrification was the rate-limiting step. Results from track study revealed that the initial specific denitrification rate (SDNR) varied between 0.6 and 1.8 mg g−1VSS hr−1. Endogenous SDNR was found to be 0.35-0.51 mg g−1VSS hr−1. Nitrogen removal was controlled mainly by the value of BOD/TN of the influent. However, the role of endogenous denitrification was relatively significant under the high mixed liquor volatile suspended solid (MLVSS) condition, making the system more robust to the fluctuation of external carbon supply. The anoxic/oxic cycle of 60/90 minutes with an hydraulic retentin time (HRT) of 10 hrs appears to be an appropriate choice for the process.

Simple device to monitor aerobic biotransformations by in situ 1H-NMR

A simple device for taking in situ proton NMR measurements in 1H2O is described. This allows aeration of reactions in a 10 mm diameter NMR tube without modifying the magnet or the probe head. With this device, aerobic biotransformations can be monitored in the NMR-tube placed in the spectrometer. It allows in situ analyses of the transformations, separating the aeration period temporally from the measurement time, not unlike traditional Warburg respiratory experiments. Two reactions determining kinetic and stoichieometric parameters: (i) a biotransformation by a growing Pseudomonas putida culture and (ii) l-phenylalanine oxidation catalysed by l-amino acid oxidase [E.C. 1.4.3.2]; both incubations were contained in the magnet.

Biological nutrient removal with an internal organic carbon source in piggery wastewater treatment

The feasibility of using an internally available carbon source for biological nitrogen and phosphorus removal was investigated. A new integrated animal wastewater treatment process consisting of two reactors was operated with various sequences for the treatment of high strength piggery manure. The treatment process was operated with real-time control technology, which utilized the oxidation–reduction potential (ORP). In the first operation, the sludge in each reactor was completely separated (sludge separation strategy, SSS), while a portion of the sludge in the first reactor was added into the second reactor in every cycle of the second operational strategy (sludge addition strategy, SAS). None of the operating strategies used a supplemental carbon source to achieve enhanced phosphorus release and denitrification. By achieving successful real-time control, very high removal efficiencies of organic matter, nitrogen and phosphorus were obtained in both operations. These high performances were mainly achieved by means of biological mechanisms, not chemical and physical processes. The real-time control made it possible to utilize an internally available organic material for phosphorus removal and denitrification of produced NO x -N, without any external carbon source. Furthermore, it was found that an optimization of aeration periods could be achieved by using the tested real-time control technology, since the technology stopped the aeration when the targeted oxidation status occurred in treatment system. The HRT obtained in both the SSS and the SAS was proportional to the F/M ratio. Experimental data showed that the sludge addition strategy (SAS) has a practical advantage over the sludge separation strategy (SSS), in that the SAS enhanced the denitrification and resulted in constant and low effluent NO x -N concentrations.

Treatment of household wastewater using an intermittently aerated membrane bioreactor

An intermittently aerated membrane bioreactor using a submerged hollow fiber membrane was applied in laboratory scale to treat household wastewater including toilet flushing water. Nitrogen removal was optimized with intermittent aeration of the reactor and adjusting the time lengths of anoxic and aerobic phases of a cycle. Membrane filtration occurred during the aeration period to take advantage of the air bubbles for fouling control. With 8–15 h HRT and a very long SRT, 96% of TCOD and 100% SS could be removed. On average, the removal efficiency for TN was 83%. No significant accumulation of inert matter was observed after 4 and 5 months of operations without sludge wasting. Fast and complete nitrification was accomplished regardless of the operation cycle mode, and denitrification appears to be the rate-limiting step. Results from track studies revealed that the specific denitrification rate (SDNR) varied between 0.6 and 1.8 mg/gVSS·h. Endogenous SDNR was determined in a separate batch experiment and found to be 0.56 mg/gVSS·h. A linear relationship between the measured SDNR and the influent BOD/TN value was found. Based on this relationship, a rule-of-thumb method to determine the optimum time length for the anoxic phase was proposed. Intermittently aerated MBR appears to have advantages over other biological nitrogen removal processes in that denitrification can be enhanced under high MLVSS conditions. Endogenous denitrification may play a significant role, making the system more robust to the fluctuation or the limitation of external carbon supply.

Enumeration and metabolic product profiles of the anaerobic microflora in the mineral soil and litter of a beech forest

Although anaerobic microorganisms can be isolated from well-drained soils, the qualitative and quantitative composition of the anaerobic populations potentially involved in the turnover of carbon in oxic soils is poorly resolved. In the present study, most probable number (MPN) estimates demonstrated that the number of anaerobes that were cultured from both forest (beech) mineral soil and litter approximated 107 to 108 (g dry wt. soil or litter)−1, a value that also approximated the number of acetate-producing anaerobes. When a complex mixture of substrates was provided, the substrate-product profiles of the MPN series indicated that the substrates that yielded the highest numbers of microbes were: yeast extract>sugars>H2>organic acids and alcohols>methoxylated aromatic compounds. Except for yeast extract, this sequence also reflected the temporal consumption of these substrates in the MPN series. The cultured anaerobic population was dominated by members of the Enterobacteriaceae and other facultative anaerobes; the facultative microorganisms appeared to determine the initial anaerobic activities of both forest soil and litter. Compared to mineral soil, litter contained more sugar-consuming anaerobes but lower numbers of butyrate-forming anaerobes. H2, ethanol, butanediol, and aromatic methoxyl groups were utilized by acetogenic bacteria. H2-utilizing acetogens were a dominant group of obligate anaerobes, attesting to the ability of acetogens to survive transient or sustained periods of aeration in habitats such as leaf litter. The numbers of cultured methanogens were negligible. Together with previous findings, these results (i) demonstrate that the formation of acetate in soils is dependent on the combined activity of facultative and obligately anaerobic microorganisms, and (ii) emphasize the potential importance of acetate as an intermediate during the turnover of carbon in habitats subject to steep oxygen gradients.

Enumeration and metabolic product profiles of the anaerobic microflora in the mineral soil and litter of a beech forest

Although anaerobic microorganisms can be isolated from well-drained soils, the qualitative and quantitative composition of the anaerobic populations potentially involved in the turnover of carbon in oxic soils is poorly resolved. In the present study, most probable number (MPN) estimates demonstrated that the number of anaerobes that were cultured from both forest (beech) mineral soil and litter approximated 10 7 to 10 8 (g dry wt. soil or litter) −1, a value that also approximated the number of acetate-producing anaerobes. When a complex mixture of substrates was provided, the substrate-product profiles of the MPN series indicated that the substrates that yielded the highest numbers of microbes were: yeast extract>sugars>H 2>organic acids and alcohols>methoxylated aromatic compounds. Except for yeast extract, this sequence also reflected the temporal consumption of these substrates in the MPN series. The cultured anaerobic population was dominated by members of the Enterobacteriaceae and other facultative anaerobes; the facultative microorganisms appeared to determine the initial anaerobic activities of both forest soil and litter. Compared to mineral soil, litter contained more sugar-consuming anaerobes but lower numbers of butyrate-forming anaerobes. H 2, ethanol, butanediol, and aromatic methoxyl groups were utilized by acetogenic bacteria. H 2-utilizing acetogens were a dominant group of obligate anaerobes, attesting to the ability of acetogens to survive transient or sustained periods of aeration in habitats such as leaf litter. The numbers of cultured methanogens were negligible. Together with previous findings, these results (i) demonstrate that the formation of acetate in soils is dependent on the combined activity of facultative and obligately anaerobic microorganisms, and (ii) emphasize the potential importance of acetate as an intermediate during the turnover of carbon in habitats subject to steep oxygen gradients.

The emission of volatile compounds during the aerobic and the combined anaerobic/aerobic composting of biowaste

Two different biowaste composting techniques were compared with regard to their overall emission of volatile compounds during the active composting period. In the aerobic composting process, the biowaste was aerated during a 12-week period, while the combined anaerobic/aerobic composting process consisted of a sequence of a 3-week anaerobic digestion (phase I) and a 2-week aeration period (phase II). While the emission of volatiles during phase I of the combined anaerobic/aerobic composting process was measured in a full-scale composting plant, the aerobic stages of both composting techniques were performed in pilot-scale composting bins. Similar groups of volatile compounds were analysed in the biogas and the aerobic composting waste gases, being alcohols, carbonyl compounds, terpenes, esters, sulphur compounds and ethers. Predominance of alcohols (38% wt/wt of the cumulative emission) was observed in the exhaust air of the aerobic composting process, while predominance of terpenes (87%) and ammonia (93%) was observed in phases I and II of the combined anaerobic/aerobic composting process, respectively. In the aerobic composting process, 2-propanol, ethanol, acetone, limonene and ethyl acetate made up about 82% of the total volatile organic compounds (VOC)-emission. Next to this, the gas analysis during the aerobic composting process revealed a strong difference in emission profile as a function of time between different groups of volatiles. The total emission of VOC, NH 3 and H 2S during the aerobic composting process was 742 g ton -1 biowaste, while the total emission during phases I and II of the combined anaerobic/aerobic composting process was 236 and 44 g ton -1 biowaste, respectively. Taking into consideration the 99% removal efficiency of volatiles upon combustion of the biogas of phase I in the electricity generator, the combined anaerobic/aerobic composting process can be considered as an attractive alternative for aerobic biowaste composting because of its 17 times lower overall emission of the volatiles mentioned.

Amonização da quirera de milho com alta umidade

O objetivo deste trabalho foi verificar o efeito da amonização sobre teor de proteína bruta (PB), retenção de nitrogênio (RN), teor de matéria seca (MS), conservação, constituintes da parede celular e digestibilidade in vitro da matéria seca (DIVMS) da quirera de milho com alta umidade (25%). Quatro níveis de amônia anidra (0, 1, 2 e 3%) e cinco períodos de aeração (0, 7, 14, 21 e 28 dias) foram estudados em delineamento inteiramente ao acaso, em esquema de parcelas subdivididas. Os teores de PB da quirera aumentaram (10,3; 14; 15,2; e 16,2%) com os crescentes dos níveis amônia anidra (0, 1, 2 e 3%). A RN diminuiu, 61,9; 39; e 31,2%, para os níveis de 1, 2 e 3% de amônia anidra, respectivamente. O teor de MS reduziu com o aumento dos níveis de amônia anidra (81,0, 77,7, 77,0 e 78,0%) e dos períodos de aeração (74,2; 75,8; 78,9; 80,3; e 80,7%). A RN (52,2 para 38,9%) e os teores de PB (14,7 para 13,5%) diminuíram com o aumento do período de aeração, respectivamente, no período de 0 a 28 dias. Houve a presença de fungos para os níveis de 0 e 1% de amônia anidra, associados a temperaturas mais altas. Os teores de fibra em detergente acido (5,6%) e celulose (4,5%) permaneceram inalterados, tanto para os niveis de amônia anidra, quanto para períodos de aeração. Os teores de fibra em detergente neutro (22,7; 22,8; 18,5; e 14,8%) e hemicelulose (17,0; 17,3; 12,7 e 9,2%) reduziram para os níveis de 0, 1, 2 e 3 % de amônia anidra, respectivamente. A DIVMS (88,5; 89,8; 90,3; e 90,8 %) da quirera de milho melhorou com o aumento dos níveis de amônia anidra (0, 1, 2 e 3%).

Nitrogen removal from synthetic wastewater by simultaneous nitrification and denitrification (SND) via nitrite in an intermittently-aerated reactor

An intermittently aerated and decanted single-reactor process was proposed and some key control parameters investigated for nitrogen removal from wastewater by simultaneous nitrification and denitrification (SND) via nitrite. Two types of synthetic wastewater with acetate as the main carbon source, and chemical oxygen demand (COD):nitrogen (N) ratios of approximately 5:1 and 10:1 were used. For both types of wastewater the average COD removal efficiency reached above 95%, and under optimal conditions nitrogen removal efficiency also reached above 90%. This process consisted of 72 min aeration, 48 min settling and 24 min effluent decanting. Influent wastewater was fed from the bottom of the reactor, and did not require a separate mixing phase. In this process, nitritation (1st step of nitrification) was induced but nitratation (2nd step of nitrification) was effectively suppressed and denitrification was carried out using nitrite. Most important parameters for effective SND via nitrite in the proposed process were: (1) the increase rate and the minimum and maximum dissolved oxygen (DO) concentration during the aeration period, (2) length of one cycle, and of aeration per cycle, taking advantage of the lag-time of nitrite-oxidizers behind ammonia-oxidizers when adjusting from anoxic/anaerobic to aerobic condition, and (3) close contact between the mixed liquor suspended solids (MLSS) in the reactor and the influent wastewater under anoxic/anaerobic condition. During the aeration period, DO concentration dropped initially reaching the minimum value after several minutes, and then rose in 2nd-order fashion. The optimal maximum DO concentration (at the end of the aeration period) for nitrogen removal was determined to be around 2.0–2.5 mg/l in this proposed process.

水耕栽培キュウリの溶存酸素濃度を異にする培地への活性炭添加が植物体の生育と収穫果実数に及ぼす効果

The effects of adding activated charcoal and different concentrations of dissolved oxygen to the hydroponic culture solution on the vegetative growth and yield of cucmber plants were studied. 1. The concentrations of dissolved oxygen in the culture solution after 6- and 24- hr aeration treatment were 1.7a3.1 ppm and 5.0a7.5 ppm, respectively. Adding activated charcoal to the culture solution with different aeration periods did not affect the concentrations of dissolved oxygen. 2. Whether the activated charcoal was added or not, the length of the primary lateral branch and its dry weight at the end of the experiment decreased slightly following 6-hr aeration compared to that following 24-hr aeration. 3. The yield per plant was unaffected by a 6-hr or 24-hr aeration but it was significantly increased by the addition of activated charcoal. Apparently root exudates, which are detrimental to vegetative growth and yield of cucumber plants are adsorbed by the activated charcoal.

Advanced analysis of membrane-bioreactor performance with aerobic-anoxic cycling

Mathematical modeling and intensive chemical analysis are used to quantify the relationships among the heterotrophic bacteria, autotrophic bacteria, and key inorganic (NH4+-N and NO3−-N) and organic (COD) compounds of municipal wastewater treated in a pilot-scale membrane bioreactor (MBR) operated with aerobic-anoxic cycles. Key features of the model for MBR are no biomass in the effluent, partial removal of biomass-associated products by the membrane, and D.O. cycling with 9 mg/L during aeration period and 0.5 mg/L for the anoxic period. The model explains the key trends in the cyclic data: NH4+-N is consumed only during aerobic periods and rises steadily during anoxic period; NO3−-N is produced only during aerobic periods, but declines in anoxic periods; The soluble COD in treated water mainly consists of BAP and is relatively constant through the cycle. Advantages of introducing an anoxic cycle to the continuous-flow MBR process are reduction of total effluent nitrogen, oxygen consumption, and sludge production as a consequence of denitrification. On the other hand, the anoxic period causes an increase in the average effluent NH4+-N.

Advanced analysis of membrane-bioreactor performance with aerobic-anoxic cycling

Mathematical modeling and intensive chemical analysis are used to quantify the relationships among the heterotrophic bacteria, autotrophic bacteria, and key inorganic (NH4+−N and NO3−−N) and organic (COD) compounds of municipal wastewater treated in a pilot-scale membrane bioreactor (MBR) operated with aerobic-anoxic cycles. Key features of the model for MBR are no biomass in the effluent, partial removal of biomass-associated products by the membrane, and D.O. cycling with 9 mg/L during aeration period and 0.5 mg/L for the anoxic period. The model explains the key trends in the cyclic data: NH4+−N is consumed only during aerobic periods and rises steadily during anoxic period; NO3−−N is produced only during aerobic periods, but declines in anoxic periods; The soluble COD in treated water mainly consists of BAP and is relatively constant through the cycle. Advantages of introducing an anoxic cycle to the continuous-flow MBR process are reduction of total effluent nitrogen, oxygen consumption, and sludge production as a consequence of denitrification. On the other hand, the anoxic period causes an increase in the average effluent NH4+−N.

Influence of oxygen on the biosynthesis of cellular fatty acids, sterols and phospholipids during alcoholic fermentation by Saccharomyces cerevisiae and Torulaspora delbrueckii

Saccharomyces cerevisiae and Torulaspora delbrueckii were grown under different O2 availabilities on grape must. Oxygen requirements for the two yeasts were different: under anaerobic conditions, S. cerevisiae produced a higher percentage of unsaturated fatty acids, and had a greater cell yield and fermentation activity than T. delbrueckii. Addition of ergosterol (25mg/l) and oleic acid (31mg/l) caused total recovery of cellular growth and the fermentation activity of S. cerevisiae in anaerobiosis, but not of T. delbrueckii. However a short period of aeration to a 48 h culture in anaerobiosis, led to total recovery of the cellular growth and fermentation activity in both yeasts. Likewise, the effect of a short aeration period on unsaturated fatty acid biosynthesis was similar for both species.

Combined treatment of landfill leachate and domestic sewage in a sequencing batch reactor

A study was undertaken to examine the feasibility of biologically treating a combined waste stream of landfill leachate and municipal sewage. The ratio of sewage to leachate was 9 to 1 by volume. The combined waste had an average BOD5 430 mg/l, COD 1090 mg/l, and TKN 133 mg/l (80% of which was in the form of ammonia). A laboratory-scale sequencing batch activated sludge reactor was used to carry comparative performance evaluations of biological treatment, including nitrification and denitrification. The SBR reactor was operating in daily time cycles employing the following sequential operation phases: filling phase, anoxic phase, aeration reaction phase, settling phase, and drain phase. In particular, the anoxic and aeration periods were tailored in order to develop conditions conducive to desired nitrification and denitrification. During the reaction period, the process was operated under an extended aeration mode with the MLSS concentration being around 3500 mg/l. The results indicated that successful biotreatment of combined leachate and sewage was possible, with the treated effluent being low in BOD5 and COD. The system was capable of BOD5 removal efficiencies exceeding 95%. Furthermore, nitrate removal during the anoxic phase was approximately 99% due to denitrification. However, the overall nitrogen removal during a full cycle was about 50%. The inclusion of an anoxic period right after the aeration phase enhanced the nitrogen removal efficiency, yet this phase required the addition of an external carbon source to the reactor due to the low concentration of biodegradable carbon, and at the same time the process became less efficient in BOD removal.

Leaching behaviors of Ni and V from spent catalyst

The leaching behaviors of Ni and V from a spent hydroprocessing catalyst were assessed in this study. The fractionations of Ni and V on the spent catalyst were determined. An automatic pH/ORP control apparatus was utilized to assess the leaching behaviors of Ni and V. When spent catalyst suspension was continuously aerated with nitrogen for 300 h, the pH did not change, and the redox potential decreased from 521 to 340 mV. Leached Ni and V concentrations did not change much during the aeration period, and were about 460 and 70 mg kg −1, respectively. The leaching experiments under equilibrium were first conducted at a pH of 5.0 and various redox potentials (− 100, 0, 100, 250, 330, 400 mV). Leached Ni concentrations did not change significantly with redox potential, while leached V concentrations decreased. At pH 8.0 and different redox potentials (− 330, − 300, − 200, − 100, 0, 150, 250 mV), leached Ni concentrations were relatively low, and increased with decreasing redox potential. Leached concentrations of V increased gradually with decreasing redox potential, and increased abruptly when the redox potential was changed from − 300 to − 330 mV. It is proposed that the exchangeable fraction of Ni was leached out, while the enhanced leaching of V could be attributed to both changes of fractionation and the reduction reactions of oxyanions of V.

Séchage intermittent de maïs en lit fluidisé à flottation : étude expérimentale et modélisation

This work concerns the drying of maize in a flotation fluidized bed by intermittent blowing of hot air. The aim of the study was on the one hand to determine the effect of this drying technique not only on the energy consumption, but also on the grain quality, and on the other hand to develop a mathematical model which simulates the observed phenomena. The effect of the conditions of intermittent drying as the duration of aeration and rest periods, respectively, t a and t r has been examined. The ratio t r t a does not affect the drying kinetics for values greater than 2. Besides, intermittent drying consumes less energy than drying with a continuous air flow because it reduces the actual drying duration by 50%. However, for the operating conditions of this study, this technique did not allow an improvement in the wet-milling quality. A mathematical model adapted to intermittent drying has been developed. This model leads to very good predictions on the evolution of air humidity, dryer temperature, grain moisture content and temperature, but also the variation of maize wet-milling and proteic qualities. This model can be used for the control of drying process under optimal conditions.

Posttreatment of Effluent from Coke-Plant Wastewater Treatment System in Sequencing Batch Reactors

The performance of sequencing batch reactors (SBRs) for the treatment of effluent from a conventional coke-plant wastewater biological treatment system has been evaluated. The results showed that an operating mode that incorporated two anoxic portions, one ahead of the aeration period and one after the aeration, was superior to the other modes (prearranged denitrification and postarranged denitrification) for nitrogen removal. The 4-h anoxic fill probably allowed some substrates in the influent to be stored in the biomass and led to subsequent storage-induced denitrification in the second anoxic portion during the reaction period. Under these conditions, the ammonia nitrogen (NH{sub 3}-N) and chemical oxygen demand (COD) reductions were 83.5 and 65.2%, respectively. During the fill period of an SBR, the organics concentration was reduced, probably due to the adsorption of organics onto activated sludge and dilution of the mixed liquor. Some readily biodegradable organics in the influent, such as phenol and o-cresol, were utilized by denitrifiers as a carbon source. A 16-h aeration significantly reduced the concentrations of o-cresol, 3,4-dimethyl phenol, and 2-quinoline alcohol, while reductions in quinoline, isoquinoline, indol, and methyl quinoline were limited.

The Operation of a Selector for the Control of Foam-Foaming Bacteria in Activated Sludge

Details are presented concerning the operation of a two-stage selector used in conjunction with an activated sludge process. The first-stage of the selector was not aerated, the second-stage had the facility for variable aeration. The prime objective of using the selector was to effect a sufficient reduction in the numbers of Microthrix parvicella to minimise the potential for the formation of stable foam in the aeration tank. In an extended trial (> 1 year) it was found that the most effective regime was when the second-stage was subjected to an aeration period of between 9 and 12 hours. It was noted that none of the changes in the aeration times had any effect on the population of the secondary filamentous species, Nostocoida limicola.

Development of the intermittent cyclic process for simultaneous nitrogen and phosphorus removal

Technology to simultaneously remove nitrogen and phosphorus from wastewater by carrying out aerobic and anaerobic operations in a single reactor has been developed by the authors. The Intermittent Cyclic Process can be used with two reactors, operating at opposite stages, to receive and treat influent on an uninterrupted basis. Research has been carried out in the: laboratory; pilot plant; and in a 540 m3 full scale wastewater plant. Experiments with aeration time ratios (aeration time to total cycle time) from 0.125 to 1 have been made, and 0.125 yielded the best nitrogen and phosphorus removal results in the laboratory study. In the pilot plant average nitrogen and phosphorus removal rates of 86% and 82% were achieved. In over three years of operation, the full-scale plant realized rates of 87% and 74% respectively. Performance has further improved with our recently developed controller which uses “fuzzy logic” to automatically determine optimal mixing and aeration periods. Measurements of DO, pH, ORP, and reactor water level are constantly relayed to the fuzzy controller. Average nitrogen and phosphorus removal rates in the full-scale plant were 96% and 93%. The study demonstrates that the fuzzy controller is practical and enhances nitrogen and phosphorus removal.

Combined treatment of landfill leachate and domestic sewage in a sequencing batch reactor

A study was undertaken to examine the feasibility of biologically treating a combined waste stream of landfill leachate and municipal sewage. The ratio of sewage to leachate was 9 to 1 by volume. The combined waste had an average BOD5 430 mg/l, COD 1090 mg/l, and TKN 133 mg/l (80% of which was in the form of ammonia). A laboratory-scale sequencing batch activated sludge reactor was used to carry comparative performance evaluations of biological treatment, including nitrification and denitrification. The SBR reactor was operating in daily time cycles employing the following sequential operation phases: filling phase, anoxic phase, aeration reaction phase, settling phase, and drain phase. In particular, the anoxic and aeration periods were tailored in order to develop conditions conducive to desired nitrification and denitrification. During the reaction period, the process was operated under an extended aeration mode with the MLSS concentration being around 3500 mg/l. The results indicated that successful biotreatment of combined leachate and sewage was possible, with the treated effluent being low in BOD 5 and COD. The system was capable of BOD5 removal efficiencies exceeding 95%. Furthermore, nitrate removal during the anoxic phase was approximately 99% due to denitrification. However, the overall nitrogen removal during a full cycle was about 50%. The inclusion of an anoxic period right after the aeration phase enhanced the nitrogen removal efficiency, yet this phase required the addition of an external carbon source to the reactor due to the low concentration of biodegradable carbon, and at the same time the process became less efficient in BOD removal.