Entrapped Mixed Microbial Cell Research Articles

Evaluation of potential integration of entrapped mixed microbial cell and membrane bioreactor processes for biological wastewater treatment/reuse

The challenge of biological wastewater treatment process is the design and operation of effective retention of mixed microbial cells within the reactor. Entrapped mixed microbial cell (EMMC) technology is designed to entrap the mixed microbial cells in polymeric carriers; membrane bioreactor (MBR) process utilizes membrane sheets/fibers to effectively retain the biomass in the reactor. These two biotechnologies are considered potential alternatives for conventional biological treatment/reuse because of their capability of retaining high concentration of biomass in the reactor, or in other words increasing the solid retention time (SRT). The simultaneous removal of organics and nitrogen were investigated using a modified EMMC system design. The modified EMMC system demonstrated higher organic and nitrogen removal performance due to high SRT. Compared to single-stage MBR process operated at similar conditions, the modified EMMC system was able to achieve slightly lower organic removal, comparable nitrification, and higher total nitrogen removal. One limitation in applying an EMMC only treatment process regime for potential reuse of treated wastewater is that such an operation requires the removal of pathogens and large particles if disinfection and solid/liquid separation were not followed. The major challenge of MBR process to overcome is membrane fouling, and the high energy consumption associated with fouling control. The intrinsic features of EMMC process including high SRT, low, and stabilized effluent suspended biomass concentration may significantly reduce the chance and extent of membrane fouling; while the membrane filtration can further polish the effluent quality from EMMC process. Therefore, integrating MBR and EMMC is strongly recommended because it may be a “break-through” for solving the membrane fouling problem and in improving effluent quality for potential reuse.

EMMC technology for treatment/reuse of dilute dairy wastewater

A rural dairy farm located on the island of Oahu, Hawaii needed to upgrade current lagoon treatment system for further reuse as floor flushing and crop irrigation. This is a comprehensive bench scale and pilot plant study to evaluate the potential biological treatment and reuse systems. Systems evaluated include: (1) pre-existing lagoon system, (2) integrated anaerobic BIO-NEST/aerobic EMMC (entrapped mixed microbial cell) system, (3) aerobic EMMC reactor only system. Based upon a comprehensive economic evaluation and sensitivity analysis, the EMMC-only system achieved the best effluent quality for simultaneous removal of carbon and nitrogen. The pilot study of the EMMC-only reactor achieved an overall of 78% TCOD, 63% SCOD, 65% TN, and 96% soluble NH3-N removal efficiencies (HRT 12 h, continuous aeration). Implementing this system would cost about $0.25 a cow/day to remove a ton of organic TCOD ($88.10/cow/year). The information presented provides a model for animal producers to consider in evaluating alternatives to upgrade existing waste management facilities.

Integrating an anaerobic Bio-nest and an aerobic EMMC process as pretreatment of dairy wastewater for reuse: a pilot plant study

A large dairy farm located on the island of Oahu, Hawaii was the site for an investigation for the potential integration of the existing facultative lagoon system with a cost effective pretreatment unit process. Based on the results from a laboratory study, a pilot plant was installed with two anaerobic bioreactors (10 m³ each) and one aerobic reactor (3.8 m³). Two layers of media “Bio-nest,” providing a void volume of 98%, were placed into each anaerobic bioreactor with 19% space-based on the bioreactor water volume. For better performance and reduction of shock-load, the equalization/settling tank was employed prior to the first anaerobic Bio-nest reactor. The intermediate holding tank settled effluent suspended solids from the Bio-nest reactor and adjusted the loading rate in order to improve the performance of the aerobic EMMC (entrapped mixed microbial cell) bioreactors. Based on the start-up operation of the Bio-nest system at an organic loading rate of about 1.5 g TCOD/l/day, the production rate of biogas from the first and second Bio-nest reactors was 0.64 and 0.15 l/l/day, respectively. This indicates that the anaerobic degradation of organics occurs mainly in the first Bio-nest reactor due to the low loading rate. The removal efficiency from the Bio-nest system shows TCOD removal of about 70%. The EMMC process provided further treatment to achieve a removal efficiency of TCOD at about 50% and a TN of about 35%. The cost for these pretreatments in order to be integrated with the existing lagoon system is US $1.1 per 1,000 gallons (3.8 m³) for dairy wastewater and $91 for each ton of TCOD removal. This integration system provides a sustainable improvement of environment and agricultural production.

EMMC process for combined removal of organics, nitrogen and an odor producing substance

In order to improve the process performance regarding the removal of organics, nitrogen, and an odor-causing compound (sulfide) contained in domestic wastewater, an entrapped-mixed-microbial cell (EMMC) with and without humic substances for both fixed and moving carrier reactors and conventional suspended growth culture (i.e. conventional activated sludge process) were investigated simultaneously. Both synthetic (simulated to the organics concentration of general domestic sewage) and actual domestic wastewater were investigated under operational conditions of 12 h of hydraulic retention time (HRT) with 1 h of aeration and 1 h of non-aeration, and 6 h of HRT with continuous aeration, at a room temperature of 25±2 °C. It was found that entrapping humic substances in the EMMC carriers had no impact on the removal of organics, nitrogen, and the odor-producing compound. Additionally, the performance of the EMMC moving carrier system for the removal of these pollutants is similar to that of the EMMC fixed carrier system. In general, the EMMC associated systems which provide high solids retention time achieve a better removal of chemical oxygen demand (COD), nitrogen, and the odor-producing substance than the suspended growth system for both HRTs of 6 h (continuous aeration) and 12 h (1 h of aeration and 1 h of non-aeration). Both the fixed and moving carrier EMMC processes, therefore, have the potential for improvement or replacement of the existing conventional activated sludge process with regard to improving the effluent qualities (such as COD, nitrogen and odor-producing compound) for reuse/disposal.

Integrating entrapped mixed microbial cell (EMMC) technology for treatment of wastewater containing dimethyl sulfoxide (DMSO) for reuse in semiconductor industries

Solvents containing dimethyl sulfoxide (DMSO) are widely used in the rinse process of stripping photoresistors in semiconductor manufacturing industries. The disposal/reuse of wastewater containing DMSO is a serious problem because of its high concentration of organic carbon and the need to suppress the odor from its sulfur contents. An entrapped mixed microbial cell (EMMC) process was used to investigate the effectiveness of removing DMSO from a synthetic wastewater in a once-through up-flow fixed-bed bioreactor. Both cellulose triacetate and cellulose acetate were used to prepare the EMMC carriers. Various hydraulic retention times (HRTs) (based on the void volume) of 3, 4, 5, 6, and 12 h were investigated when the concentration of DMSO was 500 mg/l and 1,000 mg/l. It was found that the addition of 50 mg/l of sucrose was needed to serve as the carbon source for possible co-metabolism of DMSO. Based on the result of the impact of various dilution rates (1/HRT) on the TOC (total organic carbon) removal efficiency and TOC remaining, a dilute curve for this relationship was plotted. Thus, an optimal operational criterion was developed, i.e., it must be operated at a dilution rate of less than 0.15 h−1 or at an HRT of higher than 6.66 h, in order to achieve more than 95% of TOC (or more than 99% of DMSO) removal efficiency when using the cellulose triacetate as the EMMC carriers. This process performance was compared to the bio-contact filter (BCF) process conducted in Japan. It was found that the present study is capable of producing much less effluent nitrogen (including NH4-N and NO3-N) content than the BCF process under similar loading conditions. It is possible that integrating the unit process of EMMC as pretreatment with microfiltration (MF) and reversed osmosis (RO) processes is promising for the reuse and recycling of semiconductor wastewater. Thus, higher quality (less organic carbon and inorganic nitrogen content) pretreated water can be further treated by another physical chemical process, such as MF and RO, for the production of superpurity water for reuse in the semiconductor manufacturing industry.

Integrating entrapped mixed microbial cell (EMMC) process for biological removal of carbon and nitrogen from dilute swine wastewater.

An entrapped mixed microbial cells (EMMC) process was used to investigate the simultaneous removal of carbon and nitrogen from dilute swine wastewater. Cellulose triacetate was used as the matrix for entrapping the mixed microbial cells. The EMMC process was tested with various oxygen supply conditions (ratios of aeration to non-aeration times) and two types of carrier sizes (large and medium). Also, various pre-treatments with chemical coagulation, screen separation and ammonium crystallization prior to the EMMC process, and post-treatment after the EMMC process were investigated. It was found that at a hydraulic retention time of 30 h and one hour of aeration and one hour of non-aeration, the EMMC process packed with medium carriers after the pretreatment of ammonium crystallization, exhibited the best total nitrogen removal efficiency of 95.1 +/- 1.0% when compared to the other two pre-treatment methods. The total chemical oxygen demand (TCOD) and soluble chemical oxygen demand removal efficiencies were 83.5 +/- 2.2% and 84.1 +/- 1.1%, respectively. Lime post-treatment provided TCOD and total phosphorus removal efficiencies of 59.6 +/- 2.7% and 98.0 +/- 0.5%, respectively. Thus, a cost analysis for ammonium crystallization pre-treatment, EMMC process, and post-treatment with lime was conducted. The unit cost for a 2000 pig operation is approximately dollars 4.91/pig/year. For the application of the EMMC process with the proposed pre- and post-treatments, a suitable farm size needs to be greater than a 2000 pig operation. Because of the high efficiency and the simple operation of simultaneous carbon and nitrogen removal, the EMMC process has the potential for treatment of dilute swine wastewater in a land-limited area and can be manufactured as pre-fabricated wastewater treatment units.

Entrapped mixed microbial cell process for combined secondary and tertiary wastewater treatment.

An entrapped mixed microbial cell (EMMC) process was investigated for simultaneous removal of carbon and nitrogen from a synthetic wastewater in a single bioreactor. The influent had a soluble chemical oxygen demand (SCOD)/nitrogen ratio varying from 4 to 15 and an alkalinity of 140 and 230 mg/L as calcium carbonate. An alternating schedule of intermittent aeration was used for two sizes of carriers: 10 x 10 x 10 mm3 and 20 x 20 x 20 mm3. The medium carrier (10 x 10 x 10 mm3) was found to achieve higher removals of nitrogen, chemical oxygen demand, and 5-day biochemical oxygen demand of 92, 95, and 97%, respectively. These higher removal rates occurred at a 12-hour hydraulic retention time (HRT), an aeration/ nonaeration ratio of 0.5:2 hours, and an SCOD/nitrogen ratio of 15 in the influent. Influent alkalinity concentrations of 140 and 230 mg/L as calcium carbonate were found to have minimum effect on the removal of carbon and nitrogen. However, the oxidation-reduction potential, ranging from -100 to 400 mV (during air-off period), provides better nitrogen removal efficiency to maintain the total nitrogen (nitrate, nitrite, and ammonium) less than 10 mg/L when an SCOD/nitrogen ratio of 10 or 15 is maintained in the influent. Nitrogen removal efficiency increased with increasing ratios of SCOD/nitrogen in the influent (i.e., SCOD/ nitrogen ratio of 15 > 10 > 7 > 4.0). The results of actual wastewater operation based on a study of synthetic wastewater show that organics removal efficiencies (94.6 and 94.2%) and nitrogen removal efficiencies (61.0 and 60.9%) are similar for reactors packed with medium and large carriers, respectively, when they are operated with a 9-hour HRT, an air on/air off ratio of 1 hour:2 hours and an SCOD/nitrogen ratio of 4.6.

A pilot scale bioreactor using EMMC for carbon and nitrogen removal

A pilot scale (100 l reactor) of an entrapped mixed microbial cell (EMMC) process was fabricated and tested for simultaneous removal of carbon and nitrogen. Process performance, operational stability, and maintenance requirements were all determined. Two sources of actual agricultural processing wastewater containing a high concentration of chemical oxygen demand (COD) (about 800–1,000 mg/l) and domestic sewage containing a low concentration of COD (about 150–200 mg/l) were investigated in this study. Various HRT (hydraulic retention time) and aeration schedules were operated. It was found that soluble COD (SCOD) and soluble total nitrogen (STN) could be removed in the range of 40–70% and 20–90%, respectively, for domestic sewage depending on the operational conditions provided. For agricultural processing wastewater, removal efficiencies of SCOD and STN are 89–91% and 60–75%, respectively, depending on the HRTs and aeration schedules applied. Economic evaluation for the application of domestic sewage was conducted. It was found that at an HRT of 6 h with 24 h of aeration it costs U.S.$1.75 for the treatment of 1,000 gal/day (3.8 m3/day). It is apparent that the EMMC process is technically feasible for simultaneous removal of carbon and nitrogen under the operation of an alternated schedule of the aeration in one single bioreactor. Ultimately, it can replace or upgrade the existing conventional wastewater treatment plant by combining the secondary and tertiary wastewater treatment plant in one bioreactor and provides simple maintenance and operation. This will also assist in providing the high quality of treated effluent meeting current and future environmental regulation for reuse.

Evaluation of direct removal of nitrate with entrapped mixed microbial cell technology using ethanol as the carbon source.

Biological denitrification from simulated contaminated groundwater using ethanol as an external carbon source was investigated with an entrapped mixed microbial cell (EMMC) system. Ethanol was used as an external carbon source to serve both as the energy source for the nitrate removal reaction and substrate for microorganisms in the system. The hydraulic retention time and chemical oxygen demand (COD)/nitrogen ratio significantly affect nitrate removal performance and, therefore, must be monitored carefully to achieve high rates of nitrate and COD removal. The effect of packing ratios of carriers in the reactor on nitrate removal performance was also investigated. The removal of nitrate and COD in reactors with various carrier packing ratios (12, 22, and 35%) is not significantly different during steady-state operation. However, the start-up periods in these three reactors are significantly different. The highest packing ratio can result in a fast removal of nitrate during the start-up periods. Results of solids retention time (SRT) analysis indicate that a long SRT in the EMMC system contributes to the stable removal of nitrate and to fast start up of the system. The increase of SRT is related to the increase in days of operation, SRT is maintained at a level of more than 200 days.

Development of a prefabricated treatment plant for diluted pig wastewater

In order to develop a prefabricated treatment and reuse plant for diluted pig wastewater, an entrapped‐mixed‐microbial‐cell (EMMC) process was evaluated for its process performance and economic analysis. At the hydraulic retention time (HRT) of 30 hrs (loading rate of 1.0 g TCOD/L/d) and intermittent aeration of 1 hr of aeration and 1 hr of non‐aeration, it was found that, by using the pretreatment of the ammonium crystallization, both the medium and large carriers were able to reduce TCOD, SCOD, and T‐N by 83.51, 84.11, and 95.10%, respectively. The EMMC unit and lime post‐treatment followed by ammonium crystallization can reduce BOD5, TCOD, SCOD, TSS, T‐N, and T‐P, respectively by 99.22, 93.85, 92.67, 97.73, 96.43, and 97.27%. The treated wastewater, after disinfection, is able to meet the requirements of the standards issued by the USEPA for reuse of food crops. The economic analysis indicates that based on the process performance of the EMMC unit, a prefabricated wastewater treatment plant for 2000 pigs has comparable net present worth (NPW) comparing intermittent aerated biological systems and less operation and maintenance and land requirement than conventional biological processes for removal carbon and nitrogen. A farm operation of more than 2000 pigs meets the unit cost of US$4.91/pig/yr. This will minimize the problems pertaining to technical factors or considerations that heavily influence planning, construction and operation of a pig wastewater treatment system.

Simultaneous removal of carbon and nitrogen using an entrapped-mixed-microbial-cell process

An entrapped-mixed-microbial cell (EMMC) process was investigated for its simultaneous removal of carbon and nitrogen in a single reactor which was operated on alternate schedules of aerobic, anoxic and anaerobic conditions. Two different size carrier cubes, with 20-mm (large) and 10-mm (medium) sides, were studied. The synthetic wastewater, with concentrations of 250 mg/liter of (SCOD) and 26 mg/liter of NH 4 + -N was used as influent substrate. At 25° ± 2°C, both (SCOD) and nitrogen could be removed simultaneously at 96 and 84%, respectively, for the medium carrier operated at the hydraulic retention time (HRT) of 9 h and the ratio of aeration to non-aeration of 1:2. For the large carrier, removal efficiencies of SCOD and nitrogen of 96 and 76%, respectively, were achieved under the operation at the HRT of 9 h and the ratio of aeration to non-aeration of 1:1. The low-temperature (10°C) effect on the EMMC process (both carriers) for nitrogen removal (about 47–50%) was larger than the carbon removal (92–94%). The economic analysis indicates that the EMMC process has comparable net present worth (NPW) comparing activated sludge system and less operation and maintenance and land requirement than the conventional biological processes for removal of carbon and nitrogen. Therefore, the EMMC process is suitable to be used for replacement and upgrading of existing wastewater treatment plants were land is strictly limited.

Development of a land limited wastewater treatment plant for small and rural communities in the tropics

The treatment systems for strict and moderate land limited approaches were investigated. Both synthetic glucose and actual wastewater (domestic wastewater) were studied. For the strict land limited approach, a packed entrapped mixed microbial cell (PEMMC) process using cellulose triacetate as the polymer carrier was tested for synthetic wastewater. For the moderate land limited approach, a combined aquatic weed on the water surface and a bio-fixed film in the lower portion of the pond system was investigated for both the synthetic and actual wastewater. The actual domestic wastewater was examined in a single pond system with vertical flow under the BOD5 loading rate of 135 Kg/ha/day. BOD5 and nitrogen removal efficiencies of more than 85% and 70%, respectively, were received. The glucose synthetic wastewater was examined in a single pond system with horizontal flow at a BOD5 loading rate of 130 Kg/ha/day. BOD5 and nitrogen removal efficiencies of 92% and 60%, respectively, were received. For the strict land limited treatment approach, it was found that more than 90% and 85% of soluble COD and total COD (including effluent suspended solid), respectively, could be removed at the loading rate of 1.6 g COD/L/day. The hydraulic retention time of 3.5 hours and the influent COD concentration of 200-250 mg/L were maintained and operated. This is comparable with the process performance of the conventional activated sludge for treating the domestic sewage under the same operational conditions. The PEMMC process also provides the advantages of maintaining a high SRT (Solid Retention Time) without external sludge recycling and a short starting period of less than 10 days. Application of the present two systems will be dependent on the land and/or energy requirement. It is appropriate to use the treatment system of combining the aquatic plant with the bio-fixed film for moderately available land and in tropical areas. A strict land limited treatment system, of course, requires additional energy input.

Applying entrapped mixed microbial cell techniques for biological wastewater treatment

The entrapment of mixed microbial cell was accomplished by using a porous material, such as cellulose triacetate, to confine the migration of microorganism. Synthetic glucose, phenol, carbaryl and nitrate wastewater was used as substrate to evaluate this process. Applying entrapped microbial cell techniques for biological water/wastewater treatment was previously investigated mainly by using the pure culture system. For the past six years, the University of Hawaii has investigated this technology for biological wastewater treatment by using a mixed culture approach. It was found that the developed carrier, using cellulose triacetate, is the most suitable for providing the necessary mechanical strength and durability under both the aerobic and anaerobic conditions. It also provides many advantages, such as a short start-up period, high effluent quality in terms of COD, NO3-N concentrations and removal efficiency, low effluent suspended solid concentration, and high SRT with low HRT. The process has potential to replace or upgrade the existing biological processes for water and wastewater treatment. A pre-engineered and packaged plant can be easily developed for a small wastewater treatment system for toxic or hazardous wastewater.

Packed entrapped mixed microbial cell process for removal of phenol and its compounds

Abstract Preliminary studies suggest that a bioreactor utilizing entrapped mixed microbial cells can be used to detoxify wastewaters containing pesticides such as 1‐naphthyl N‐methylcarbamate. Mixed cultures were obtained from soil samples. Performance of entrapped cells is compared with that of similar cultures adsorbed on cellulose triacetate fibers.