Effects of coupling a UF membrane with a mesh screen and elevating temperature in the methanogenic digester of a two-phased anaerobic system.

This study was conducted to investigate coupling of UF with a mesh screen under thermophilic temperatures and compare the effectiveness of membrane filtration and temperature change in the methanogenic digester. A two-phased anaerobic digester coupled with an ultrafiltration (UF) membrane system was used for anaerobic sludge digestion. The overall average chemical oxygen demand (COD) removal efficiency achieved in the two-phased anaerobic digester coupled with the UF membrane system was 97.9 ± 0.8%. In the methanogenic digester, 10.5% improvement of methane production rate was obtained by the increased microbial population and metabolic activity due to coupling with a UF membrane and a mesh screen and elevating the temperature from mesophilic to thermophilic conditions. The average methane production per VS loading and unit volume (m3) was 477.14 ± 31.5 and 567.15 ± 43.3 mL CH4g-1 VS before and after elevating the temperature, respectively. The optimal operating pressure for the UF membrane system was less than 3 kgf cm-2, and the mesh screen saved 19.0% of the operating cost and 17.3% of energy consumption. As a result, the UF membrane system enhanced the digestion of sewage sludge, where the elevation of temperature improved the methane production rate in the thermophilic methanogenic digester.

Control of membrane fouling with the addition of a nanoporous zeolite membrane fouling reducer to the submerged hollow fiber membrane bioreactor.

The membrane fouling control via the addition of nanoporous zeolite membrane fouling reducer (Z-MFR) to the submerged membrane bioreactor (MBR) was investigated. Using scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis techniques, the characteristics of fouling on a hollow fiber membrane surface were also analyzed. The addition of Z-MFR to the MBR led to the adsorption of foulants and the flocculation of mixed liquor suspended solids (MLSSs), which resulted in substantially enhancing the membrane filterability. The critical flux values obtained from the sewage mixed liquors of 3400 mg L(-1) at the effective dosage rate of 0.03 mg Z-MFR mg(-1) MLSS was 85 L m(-2) h(-1) (LMH), which was enhanced by 42%. The transmembrane pressure (TMP) variation under the operating conditions of 30 LMH with 3500 mg MLSS L(-1) showed that the addition of Z-MFR extended the time required to reach the critical flux of 0.32 bar by 2.6-fold longer than the control. Thus, due to the hybrid functions of adsorbing foulants and precipitating colloidal substances with the addition of Z-MFR, a decrease in the foulant amount and an improvement of sludge flocculation have been attained simultaneously. As a result, the membrane fouling control was achieved effectively with the addition of the Z-MFR.

Simultaneous attenuation of pharmaceuticals, organic matter, and nutrients in wastewater effluent through managed aquifer recharge: Batch and column studies.

Batch and column experiments were conducted to evaluate the removal of organic matter, nutrients, and pharmaceuticals and to identify the removal mechanisms of the target contaminants. The sands used in the experiments were obtained from the Youngsan River located in South Korea. Neutral and cationic pharmaceuticals (iopromide, estrone, and trimethoprim) were removed with efficiencies greater than 80% from different sand media during experiments, due to the effect of sorption between sand and pharmaceuticals. However, the anionic pharmaceuticals (sulfamethoxazole, ketoprofen, ibuprofen, and diclofenac) were more effectively removed by natural sand, compared to baked sand. These observations were mainly attributed to biodegradation under natural conditions of surface organic matter and ATP concentrations. The removal of organic matter and nitrogen was also found to increase under biotic conditions. Therefore, it is indicated that biodegradation plays an important role and act as major mechanisms for the removal of organic matter, nutrients, and selected pharmaceuticals during sand passage and the managed aquifer recharge, which is an effective treatment method for removing target contaminants. However, the low removal efficiencies of pharmaceuticals (e.g., carbamazepine and sulfamethoxazole) require additional processes (e.g., AOPs, NF and RO membrane), a long residence time, and long travel distance for increasing the removal efficiencies.

Alginate fouling reduction of functionalized carbon nanotube blended cellulose acetate membrane in forward osmosis.

Functionalized multi-walled carbon nanotube blended cellulose acetate (fCNT-CA) membranes were synthesized for forward osmosis (FO) through phase inversion. The membranes were characterized through SEM, FTIR, and water contact angle measurement. AFM was utilized to investigate alginate fouling mechanism on the membrane. It reveals that the fCNT contributes to advance alginate fouling resistance in FO (57% less normalized water flux decline for 1% fCNT-CA membrane was observed than that for bare CA membrane), due to enhanced electrostatic repulsion between the membrane and the alginate foulant. Furthermore, it was found that the fCNT-CA membranes became more hydrophilic due to carboxylic groups in functionalized carbon nanotube, resulting in approximately 50% higher water-permeated flux than bare CA membrane. This study presents not only the fabrication of fCNT-CA membrane and its application to FO, but also the quantification of the beneficial role of fCNT with respect to alginate fouling in FO.

Implementation of an excess sludge reduction step in an activated sludge process.

In this study, excess sewage sludge reduction resulting from the modification of an activated sludge process by incorporation of an excess sludge digesting reactor (ESDR) was examined. The ESDR was coupled to the sludge return line, and enhanced the solubilization of cell mass under thermophilic aerobic conditions. The decrease in the level of total suspended solids (TSS) observed in the reference ESDR (without thermophilic microbial inoculation) was 13.76% whereas a TSS decrease of 32.09% was achieved by the test ESDR (with thermophiles), thus showing microbial enhancement of solubilization of 18.33% over a test period of 48 h. The average excess sludge solubilization ratios (beta values) of TSS were 51.17% and 41.56% in two distinct protocols varying in operative parameters. The calculated excess sludge reduction ratio was 49.60% with a sludge recirculation ratio of 2, but increased to 68.97% when the sludge recirculation ratio rose to 3. The sludge volume indexes (SVIs) for the control and test processes were 68.4 and 57.0 respectively, indicating the absence of any negative effect of the modification on sludge settling characteristics. Effluent water quality satisfied national legislative requirements.

Biodegradation of high molecular weight lignin under sulfate reducing conditions: lignin degradability and degradation by-products.

This study is designed to investigate the biodegradation of high molecular weight (HMW) lignin under sulfate reducing conditions. With a continuously mesophilic operated reactor in the presence of co-substrates of cellulose, the changes in HMW lignin concentration and chemical structure were analyzed. The acid precipitable polymeric lignin (APPL) and lignin monomers, which are known as degradation by-products, were isolated and detected. The results showed that HMW lignin decreased and showed a maximum degradation capacity of 3.49 mg/l/day. APPL was confirmed as a polymeric degradation by-product and was accumulated in accordance with HMW lignin reduction. We also observed non-linear accumulation of aromatic lignin monomers such as hydrocinnamic acid. Through our experimental results, it was determined that HMW lignin, when provided with a co-substrate of cellulose, is biodegraded through production of APPL and aromatic monomers under anaerobic sulfate reducing conditions with a co-substrate of cellulose.

Expression of heat shock protein and hemoglobin genes in Chironomus tentans (Diptera, chironomidae) larvae exposed to various environmental pollutants: a potential biomarker of freshwater monitoring.

To identify a sensitive biomarker of freshwater monitoring, we evaluated pollutant-induced expression of heat shock proteins (HSPs) and hemoglobins (Hbs) genes in the larvae of the aquatic midge Chironomus tentans (Diptera, Chironomidae). As pollutants, we examined nonylphenol, bisphenol-A, 17alpha-ethynyl estradiol, bis(2-ethylhexyl) phthalate, endosulfan, paraquat dichloride, chloropyriphos, fenitrothion, cadmium chloride, lead nitrate, potassium dichromate, benzo[a]pyrene and carbon tetrachloride. We also investigated larval growth as a physiological descriptor by measuring changes in the body fresh weight and dry weight after chemical exposure. The response of the HSPs gene expression by chemical exposure was rapid and sensitive to low chemical concentrations but it was not stressor specific. Interestingly, an increase in the expression of HSPs genes was observed not only in a stress inducible form (HSP70), but also in a constitutively (HSC70) expressed form. The expression of Hb genes showed chemical-specific responses: that is, alkyl phenolic compounds increased the expression of hemoglobin genes, whereas pesticides decreased the expression. As expected, molecular-level markers were more sensitive than physiological endpoints, suggesting that gene expression could be developed as an early warning biomarker in this animal. The overall results suggest that the expression of HSP and Hb genes in Chironomus could give useful information for diagnosing general health conditions in fresh water ecosystem. The expression of Hb genes, in particular, seems to be a promising biomarker, especially in view of the potential of Chironomus larvae as a biomonitoring species and of the physiological particularities of their respiratory pigments.

Examination of mechanisms for odor compound generation during lime stabilization.

Lime-stabilized biosolids produced from a wastewater treatment plant often emit odors, especially those described as "fishy" and "decaying". These odors can generate public opposition to biosolids land-application programs even though they represent an environmentally friendly recycling of organic material that is beneficial to the agricultural industry. Therefore, it is critical to examine the controlling factors involved in odor production during the lime stabilization process. Results from preliminary experiments examining added polymer and protein material to dewatered limed biosolids show increased trimethylamine (TMA) production with further increases in 1-hour and 4-hour storage times prior to liming. Further experiments with water-silica slurry reaction media reveal that enzymatically facilitated degradation of polymer and protein is the overriding factor in TMA and dimethyldisulfide (DMDS) production. It is hypothesized that macromolecules such as polymer and proteins in biosolids are first broken down enzymatically, upon which the addition of lime causes TMA and DMDS to be released.