Intermittent Aeration Mode Research Articles

Application of biofilm membrane bioreactor and Reverse Osmosis membrane to the treatment of fresh and partially stabilised leachate

Membrane Bioreactor (MBR) with sponge cube media and reverse osmosis (RO) were investigated in laboratory scale. Fresh and partially stabilised leachate contained COD/N of 30 and 10 and BOD/COD of 0.7-0.9 and 0.4-0.7, respectively. Continuous and intermittent aeration modes were examined. COD and TKN removals were more than 90%. Highest nitrogen removal efficiency was achieved when aeration of 1 h on and 2 h off cycle were employed. The effluent from MBR was further treated in RO unit with average rejection efficiencies of 75% 97%, 94% and 99% for COD, NH4+, SO42− and PO43−, respectively.

The pathway of in-situ ammonium removal from aerated municipal solid waste bioreactor: nitrification/denitrification or air stripping?

In-situ ammonium removal from municipal solid waste (MSW) landfill is an attractive method due to its economic advantages. In this study, two simulated MSW bioreactors with different degrees of initial bio-stabilization were utilized to investigate the effects of intermittent aeration mode and the addition of activated sludge on the removal of ammonium. The results showed that up to 90% of ammonium could be removed and the amount of NO(x)-N produced was less than 1% of NH4 (+)-N removed in both reactors. The pH values increased rapidly and finally arrived at a high level of 8.5-8.8. The efficiency of ammonium removal was improved by increasing the continuous aeration time, but it was not affected by the addition of activated sludge. A portion of liquid escaped from the reactors in the form of vapour, and as high as 195-258 mg L(-1) of NH(4) ( +)-N was detected in the vapour collector. According to calculation, nitrification was inhibited by the high level of free ammonia in the bioreactors. As a result, air stripping was enhanced and became the primary pathway of ammonium removal. Therefore, controlling free ammonia concentration was essential in ammonium removal from the aerated MSW bioreactor.

Performance of Biological Powder Activated Carbon-Membrane Bioreactor (BPAC-MBR) for old-landfill leachate treatment

This research aims to investigate the performance of the combined BPAC-MBR system for old-landfill leachate treatment. The system was operated at two different intermittent aeration modes (aeration or non-aeration) of 120-120 min and 150-150 min. It was found that the BPAC-MBR system operating at 150-150 min could give higher removal efficiencies for all parameters; COD at 83%, colour at 85%, TKN at 97%, and TP at 68%. The reason might be that the degradation mechanism of microorganisms inside the BPAC-MBR system needed sufficient time for sequential aerobic and anaerobic periods to improve biodegradation for slowly biodegradable organic compounds.

Bioaugmentation이 간헐폭기 오수처리장치의 운전효율에 미치는 영향

In order to improve reactor performance of existing sewage treatment plants, the feasibility of enhancing reactor performance by bioaugmentation using EM as bioaugmentation agent and the effects of anoxic: oxic time ratio on reactor performance were investigated. Continuous and intermittent aeration modes were compared under the 6 hr of HRT. Three different types of intermittent aeration modes, that is, 15 min, of anoxic:45 min of oxic, 30 min of anoxic: 30 min of oxic, and 45 min of anoxic: 15 min oxic respectively were chosen as test modes to study the effects of anoxic : oxic time ratios on reactor performance. The optimum anoxic: oxic time ratio was 30 min:30 min when considering simultaneous removal of organic, nitrogen and phosphorus. When applying EM into a continuously aerated reactor under the varying dosing rates of 50-200 ppm, reactor performance in terms of organic and nitrogen removal efficiencies was not improved at all. Nitrogen removal efficiency was increase when the EM dosing rate was increased. However the degree of improvement was slight when the EM was injected above 100 ppm. However optimum phosphorus removal was found at the EM dosing of 200 ppm. Thus it was found that optimum injection concentration of EM is 200 ppm. It is apparent that putting EM into a sewage treatment plant significantly affects the T-N removal efficiency of the reactor by enhancing denitrification efficiency especially in operational conditions of relatively long anoxic periods. To achieve reciprocal condition in a reactor with intermittent aeration it is necessary to enhance the reactor performance by EM injection. In the case of modifying existing continuously aerated reactors into intermittent aerated reactors, it is obvious that operating costs of aeration would be reduced by reducing aeration time when compared with existing conventional sewage treatment plants.

Performance of solid waste digestion and bacterial monitoring in landfill bioreactor with intermittent aeration mode

Performance of solid waste digestion and bacterial monitoring in landfill bioreactor with intermittent aeration mode

Characterization of efficient aerobic denitrifiers isolated from two different sequencing batch reactors by 16S-rRNA analysis

By adopting two sequencing batch reactors (SBRs) A and B, nitrate as the substrate, and the intermittent aeration mode, activated sludge was domesticated to enrich aerobic denitrifiers. The pHs of reactor A were approximately 6.3 at DOs 2.2-6.1 mg/l for a carbon source of 720 mg/l COD; the pHs of reactor B were 6.8-7.8 at DOs 2.2-3.0 mg/l for a carbon source of 1500 mg/l COD. Both reactors maintained an influent nitrate concentration of 80 mg/l NO3- -N. When the total inorganic nitrogen (TIN) removal efficiency of both reactors reached 60%, aerobic denitrifier accumulation was regarded completed. By bromthymol blue (BTB) medium, 20 bacteria were isolated from the two SBRs and DNA samples of 8 of these 20 strains were amplified by PCR and processed for 16SrRNA sequencing. The obtained results were analysed by a Blast similarity search of the GenBank database, and constructing a phylogenetic tree for identification by comparison. The 8 bacteria were found to belong to the genera Pseudomonas, Delftia, Herbaspirillum and Comamonas. At present, no Delftia has been reported to be an aerobic denitrifier.

Optimization of Nitrogen Removal for Alternating Intermittent Aeration-Type Activated Sludge System: A New Process Modification

A new activated sludge process modification was proposed for intermittent aeration process to achieve more stable nitrogen removal performance. A single completely mixed reactor was divided into two compartments in series and operated in intermittent aeration mode by using activated sludge simulation model. The new configuration provided competetive advantage on nitrification as well as denitrification capacity, compared to the intermittently aerated system with a single reactor. In addition, the dissolved oxygen set-point control during air-on periods was found to be an important parameter in terms of nitrogen removal.

Dissolved organic matter (DOM) in recycled leachate of bioreactor landfill

Landfill leachate needs sufficient treatment before safe disposal. Bioreactor landfill technology could effectively degrade the organic matters in recirculated leachate, hence leaving a leachate stream of low biodegradability. This study characterized the dissolved organic matter (DOM) in the leachate from simulated bioreactor landfill columns with or without presence of trace oxygen. The removal efficiencies of this DOM using coagulation–sedimentation or electrolysis processes were demonstrated. Recirculated leachates were sampled from the simulated landfill columns applying conventional mode, intermittent-aeration mode, and natural aeration mode, whose DOM was fractionated into humic acids (HA), fulvic acids (FA) and hydrophilic fractions (HyI) by the XAD-8 resin combined with the cation exchange resin method. The recirculated leachate had low BOD/COD ratio, high humic substances contents, and high aromatic content. Their HA fraction comprised mainly large molecules (>10 k Da), while the FA and HyI were composed of smaller molecules (<50 k and <4 k Da, respectively). With the presence of oxygen, the TOC contents and the contents of HA, FA and HyI in leachate reduced, with FA and HyI fractions of molecular weight (MW) lower than 4 k Da more readily degraded. The organic matters left in leachates from intermittent-aeration mode and natural aeration mode were of low biodegradability. It was tested in the following sections the effects of coagulation–sedimentation process and of electrolysis process on the removal of residual DOM in recirculated leachate. Coagulation–sedimentation tests revealed that poly ferric sulphate (PFS) could remove more COD (58.1%) from leachate than polyaluminum chloride (PACl) (22.9%), particularly on the HA fraction with MW>10 k Da. Coagulation–sedimentation could not remove most of HyI in leachate. Furthermore, the corresponding BOD/COD ratio was not improved through coagulation. Electrolysis test could also effectively removed HA of MW>10 k Da. However, the biodegradability of treated effluent considerably was improved. The electrolysis could decompose high MW substances and increase biodegradability of recirculated leachate from bioreactor landfill.

Simultaneous Removal of Carbon and Nitrogen from Swine Wastewater Using an Immobilized-Cell Reactor

A single-stage phosphorylated polyvinyl alcohol immobilized-cell reactor with three operation modes was employed to investigate the efficiency of simultaneous carbon/nitrogen removal from raw swine wastewater. In continuous aeration mode, the removal efficiency of chemical oxygen demand (COD) and total nitrogen (T-N) exceeded 70 and 8%, respectively, at hydraulic retention time of 10 days. In intermittent aeration (IA) mode, the removal efficiency of COD and T-N was more than 85 and 46%, respectively, when the reactor was set at 50% aeration duration to cycle time to operate at three aerobic-anoxic cycles per day. When oxidation-reduction-potential control was adopted to control the duration of the anoxic period in the real-time controlled (RTC) IA mode for a 4 h aeration period, the total cycle time was reduced by about 20% with a slight increase in removal efficiency of COD (87%) and T-N (47%). The system with no extra chambers required is efficient in simultaneous carbon/nitrogen removal.

High levels of nitrifying bacteria in intermittently aerated reactors treating high ammonia wastewater

Changes in the fractions of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in two laboratory-scale reactors were investigated using 16S rRNA probe hybridizations. The reactors were operated in intermittent aeration mode and different aeration cycles to treat anaerobically digested swine wastewater with ammonia concentrations up to 175 mg NH 3-N/L. High ammonia removals (>98.8%) were achieved even with increased nitrogen loads and lower aeration: non-aeration time ratios of 1 h:3 h. Nitrosomonas/ Nitrosococcus mobilis were the dominant ammonia-oxidizing bacteria in the reactors. Nitrospira-like organisms were the dominant nitrite-oxidizing bacteria during most of the investigation, but were occasionally outcompeted by Nitrobacter. High levels of nitrifiers were measured in the biomass of both reactors, and ammonia-oxidizing bacteria and nitrite-oxidizing bacterial levels adjusted to changing aeration: non-aeration time ratios. Theoretical ammonia-oxidizer fractions, determined by a mathematical model, were comparable to the measured values, although the measured biomass fractions were different at each stage while the theoretical values remained approximately constant. Stable ammonia removals and no nitrite accumulation were observed even when rRNA levels of ammonia oxidizers and nitrite-oxidizers reached a minimum of 7.2% and 8.6% of total rRNA, respectively. Stable nitrogen removal performance at an aeration: non-aeration ratio of 1 h:3 h suggests the possibility of significant savings in operational costs.

The effect of reactor configuration and operational mode on Microthrix parvicella bulking and foaming in nutrient removal activated sludge systems

Three bench-scale nutrient removal activated sludge units were used to examine the effect of the reactor configuration and the intermittent aeration mode on the growth of Microthrix parvicella. According to the results, the plug flow configuration seems to achieve satisfactory Microthrix parvicella control. The imposed concentration gradient for both RBCOD and SBCOD creates a selective advantage for the floc forming bacteria throughout the system (both the anoxic and oxic zones) and limits Microthrix parvicella growth. In terms of the operational mode, the intermittent aeration CSTR nutrient removal system promotes the growth of M. parvicella and deteriorates the settling characteristics of the activated sludge.

ORGANIC MATTER AND NITROGEN REMOVAL IN ROTARY DISK TYPE UF MEMBRANE BIOREACTOR FOR FERMENTATION WASTEWATER TREATMENT

Various intermittent aeration modes were applied to treat fermentation wastewater by highly concentrated activated sludge process coupled with OF membrane. Organic removal did not decrease significantly compared with continuous aeration mode. Denitrification contributed most to T-N removal compared with T-N losses in sample and sludge synthesis, and the optimal operating condition (30-min. aeration on and 30-min. aeration off) was obtained for carbon and nitrogen removals. Fluctuation patterns of DO and ORP in a cycle were observed and the activity of sludge was assessed by INT-dehydrogenase activity. Based on SEM observation, the rod-type bacteria were predominant compared with filamentous bacteria at higher MLSS concentration.

Performance evaluation of on-site treatment facilities for wastewater from Households, Hotels and Restaurants

In order to evaluate performance of on-site treatment facilities which can be provided for environment protection in coastal areas, effluent qualities and removal efficiencies were surveyed in actual treatment facilities for wastewater from households, hotels and restaurants. On-site treatment facilities in Japan are fundamentally built according to the structural standards. They have a pretreatment process (sedimentation separation tank, anaerobic filter or equalization tank with screens) followed by an aerobic process (contact aeration, activated sludge, etc.). Small-scale facilities for individual household wastewater showed good performance of BOD removal with their effluent BOD below 20mg 1−1. They also exhibited nitrogen removal efficiency when they were operated in mixed liquor recycle mode. The facilities applied to wastewater from hotels, restaurants and stores showed good performance when the influent oil (hexane extracts) concentration had been decreased below 30mg 1−1 by using pretreatment. Nitrogen removal performance was high in the facilities which treated wastewater from a residential area or a condominium when they were operated in intermittent aeration mode. But resort condominiums of which influent BOD load was extremely low showed low performance of nitrogen removal even though they were operated in intermittent aeration mode because of the low BOD/N ratio in the influent. An equation was proposed to estimate the amount of methanol to be added in facilities in which the influent BOD/N ratio is low.

Performance evaluation of on-sitetreatment facilities for wastewater from households, hotels and restaurants

In order to evaluate performance of on-site treatment facilities which can be provided for environment protection in coastal areas, effluent qualities and removal efficiencies were surveyed in actual treatment facilities for wastewater from households. hotels and restaurants. On-site treatment facilities in Japan are fundamentally built according to the structural standards. They have a pretreatment process (sedimentation separation tank, anaerobic filter or equalization tank with screens) followed by an aerobic process (contact aeration, activated sludge, etc.). Small-scale facilities for individual household wastewater showed good performance of BOD removal with their effluent BOD below 20mg I −1. They also exhibited nitrogen removal efficiency when they were operated in mixed liquor recycle mode. The facilities applied to wastewater horn hotels, restaurants and stores showed good performance when the influent oil (hexane extracts) concentration had been decreased below 30mg 1 −1 by using pretreatment. Nitrogen removal performance was high in the facilities which treated wastewater from a residential area or a condominium when they were operated in intermittent aeration mode. But resort condominiums of which influent BOD load was extremely low showed low performance of nitrogen removal even though they were operated in intermittent aeration mode because of the low BOD/N ratio in the influent. An equation was proposed to estimate the amount of methanol to be added in facilities in which the influent BOD/N ratio is low.

生活排水の断続曝気処理施設における低負荷運転時の窒素除去特性

The water quality before and after the secondary treatment in domestic wastewater treatment facilities in Chiba prefecture Japan were surveyed. T-N removal performance was high in the plants operated in intermittent aeration mode as compared with those operated in continuous aeration mode because of occurence of biological denitrification in their process. The performance of T-N removal was low in the facilities of which influent BOD concentration was low even though it was operated in intermittent aeration mode. The decease of BOD was observed in equalization tanks in the facilities of resort condominiums of which influent BOD load was extremely low. The mean value of influent BOD/T-N ratio in such facilites was below 2. That caused lack of proton donor resulting in difficulty in progress of denitrification while nitrification was advanced sufficiently. The relation between influent BOD/T-N ratio and T-N removal in surveyed 37 facilities suggested that the maximum T-N removal for a certain value of BOD/T-N ratio smaller than 4 decreased by the equation approximately: RN,Max=20×(BOD/T-N)+10, where RN,Max is the maximum T-N removal(%). This equation can be applied to estimate the amounts of proton donor to be added in facilities of which influent BOD/T-N ratio is low.

Ｕチューブ型膜分離深層曝気槽におけるし尿の硝化脱窒特性に関する研究

The effects of BOD5/TKN ratio in raw night soil and dissolved oxygen concentration in a U-tube bioreactor on nitrogen removal and N2O formation were studied using a single-sludge acivated sludge system including a U-tube bioreactor with a membrane filter for the separation of activated sludge from purified night soil. The advantage of this system is that high nitrogen removal efficiency is achieved even at a low BOD5/TKN ratio in night soil without additional carbon source by the high MLSS (average MLSS of approximately 20 kg·m-3) operation. Night soil treated by the U-tube bioreactor in a pilot plant had an average BOD5/TKN ratio of 1.75. It was found out that accumulation of NO2- in the U-tube bioreactor, high N2O formation and inhibition of nitrifying organisms took place at BOD5/TKN ratio of 2 in night soil by the conventional intermittent aeration mode in which the dissolved oxygen concentration was kept over 2 mg·l-1 during the aerobic period. However, the reduction of NOx-N and control of N2O formation were achieved completely by the low dissolved oxygen concentration (between 0 and 1 mg·l-1) mode in which the average BOD5/TKN ratio and TKN load were 1.75 and 0.05 kg·kg-1·d-1, respectively.

Organic stabilisation and nitrogen removal in a membrane separation bioreactor for domestic wastewater treatment

Organic stabilization and nitrogen removal wore investigated using a hollow fibre membrane separation bioreactor of 62 I volume. The process employed was direct solid-liquid separation by the hollow fibre membrane inside an activated sludge aeration tank. By providing highly turbulent conditions within the separation zone and incorporating a jet aerating installation inside the membrane module, sludge accumulation on the membrane surface and inside the module can be reduced. Permeate flux obtained after 330 days of operation was 0.2 m/d under intermittent auction. A high degree of organic stabilisation was obtained in the system without sludge wastage except for sampling purposes. Continuous and intermittent aeration modes were investigated. Average effluent COD concentrations of 20.8 and 16.5 mg/I were observed during continuous and intermittent aeration, respectively. The degree of nitrification depended on the DO concentration of the mixed liquor during the aerating period. Introduction of intermittent aeration enhanced total nitrogen removal up to 80% or more by simultaneous nitrification and denitrification, resulting in an average value of 4.9 mg/I of total nitrogen in the effluent. Increasing the DO in the aerating period from 1.5 – 2 mg/I to 4 – 5 mg/I increased nitrogen removal to more than 90%. Rejection of 4 – 6 log virus concentration by a gel layer formed on the membrane surface was also observed.

Organic Stabilization and Nitrogen Removal in Membrane Separation Bioreactor for Domestic Wastewater Treatment

In this study, organic stabilization and nitrogen removal were investigated using a household type hollow fiber membrane separation bioreactor of 6 2 1 volume. The process employed direct solid-liquid separation by hollow fiber membrane inside an activated sludge aeration tank. By providing highly turbulent conditions within the separation zone in conjunction with Jet aerating installation inside the membrane module, sludge accumulation on the membrane surface and inside the module can be reduced. Permeate flux obtained after 330 days of operation was 0.2 m/d under intermittent suction. High degree of organic stabilization was obtained in the system by operation without sludge wastage except for sampling purposes. Continuous and intermittent aeration modes were investigated in the study. The average effluent COD concentration of 20.8 and 16.5 mg/l were observed during continuous and intermittent aerating application respectively. Degree of nitrification depended upon DO concentration of mixed liquor during aeration period. Introduction of intermittent aeration enhanced total nitrogen removal up to 80% or more by simultaneous nitrification and denitrification, resulting in average of 4.9 mg/l of total nitrogen in the effluent. Increase in DO in aeration period from 1.5–2 mg/l to 4–5 mg/l improved percentage of nitrogen removal to more than 90%. Rejection of 4–6 log virus concentration by gel layer formed on the membrane surface was also observed.

Practical Performance of Nitrogen Removal in Small-Scale Sewage Treatment Plants Operated in Intermittent Aeration Mode

Research was carried out to clarify the number and the scale of small-scale sewage treatment plants operated in intermittent aeration mode by asking questions to maintenance workers in Chiba Prefecture, Japan. The percentage of the number of plants operated in intermittent aeration mode was 26.5%. This percentage was high in the plants larger than 200 population equivalent (p.e.). The practical performance of nitrogen removal was evaluated in nine existing plants operated in intermittent aeration mode. A high performance of nitrogen removal was noticed in the plants us ing extended aeration process. The performances of nitrogen removal in two plants operated in intermittent aeration mode were compared with those operated in continuous aeration mode. The characteristics of denitrification taking place in the aeration tank in a plant operated in intermittent mode were investigated by measuring the change in nitrogen concentration in the tank during the intermittent period. The seasonal performanee of denitrification was studied by a long term practical experiment for 16 months. By operating the length of intermittent time according to the change of the water temperature in the aeration tank, a high performance of nitrogen removal was obtained throughout the year.

A pilot-scale evaluation of aerobic–anoxic sludge digestion

A pilot-scale (300 L) evaluation of waste-activated sludge digestion by a cyclical aerobic–anoxic mode of operation was undertaken at ambient liquid temperatures (14–17 °C). Three experimental runs were conducted over a 2-year period. The first run compared the aerobic–anoxic process to a conventional, continuously aerated, digestion process. During the second run, the aerobic–anoxic digester was compared to a lime-supplemented conventional aerobic process. The third run compared two aerobic–anoxic digester units, operating at reduced (50 and 25% of normal) aeration rates during the aerobic period. In addition, basic data from batch tests are outlined and discussed. Results from the various experimental runs indicated numerous potential advantages for the aerobic–anoxic mode of digester operation. The main advantage was that turning the air on and off resulted in volatile solids reduction efficiencies similar to that in the continuously aerated systems. In addition to the potential for significant savings in aeration costs, another benefit of the intermittent aeration mode of operation involved improved supernatant quality of the final, settled effluent. Key words: aerobic digestion, anoxic, intermittent aeration, lime, pilot-scale, Redox potential, sludge, solids reduction.