Oxygen transport across the capillary fringe in LNAPL pool-source zones

Transfer of oxygen across the capillary fringe and water table is a critical oxygen source for aerobic biodegradation of hydrocarbon light nonaqueous phase liquids (LNAPLs) at or near the water table. However, significant resistance to oxygen mass transfer may be associated with the capillary fringe. This work evaluates the hypothesis that a decrease in the water-saturated thickness of the capillary fringe due to the presence of a hydrocarbon LNAPL, and the reduced resistance to oxygen mass transfer in the hydrocarbon phase, will enhance oxygen transfer relative to natural reaeration. Oxygen flux in the absence and presence of an LNAPL pool is conceptually evaluated using the two-film model. Abiotic experiments in a bench-scale sand-tank reactor demonstrated that oxygen transport through the water table interface was enhanced when an LNAPL (dodecane) pool was present at the water table compared to natural reaeration. Biotic experiments demonstrated that the increased oxygen transport in the presence of the LNAPL pool also increased biodegradation of a solute (glucose) plume passing beneath the LNAPL pool. Biodegradation also apparently further bioenhanced the oxygen transfer

Effects of organic loading rates on reactor performance and microbial community changes during thermophilic aerobic digestion process of high-strength food wastewater

To evaluate the applicability of single-stage thermophilic aerobic digestion (TAD) process treating high-strength food wastewater (FWW), TAD process was operated at four organic loading rates (OLRs) from 9.2 to 37.2 kg COD/c d. The effects of OLRs on microbial community changes were also examined. The highest volumetric removal rate (13.3 kg COD/m(3) d) and the highest thermo-stable protease activity (0.95 unit/mL) were detected at OLR = 18.6 kg COD/m(3) d. Denaturing gradient gel electrophoresis (DGGE) profiles and quantitative PCR (qPCR) results showed significant microbial community shifts in response to changes in OLR. In particular, DGGE and phylogenetic analysis demonstrate that the presence of Bacillus sp. (phylum of Firmicutes) was strongly correlated with efficient removal of organic particulates from high-strength food wastewater. (C) 2013 Elsevier Ltd. All rights reserved.11sciescopu

Microbial community structure in a thermophilic aerobic digester used as a sludge pretreatment process for the mesophilic anaerobic and the enhancement of methane production

An effective two-stage sewage sludge digestion process, consisting of thermophilic aerobic digestion (TAD) followed by mesophilic anaerobic digestion (MAD), was developed for efficient sludge reduction and methane production. Using TAD as a biological pretreatment, the total volatile suspended solid reduction (VSSR) and methane production rate (MPR) in the MAD reactor were significantly improved. According to denaturing gradient gel electrophoresis (DGGE) analysis, the results indicated that the dominant bacteria species such as Ureibacillus thermophiles and Bacterium thermus in TAD were major routes for enhancing soluble organic matter. TAD pretreatment using a relatively short SRT of 1 day showed highly increased soluble organic products and positively affected an increment of bacteria populations which performed interrelated microbial metabolisms with methanogenic species in the MAD; consequently, a quantitative real-time PCR indicated greatly increased Methanosarcinales (acetate-utilizing methanogens) in the MAD, resulting in enhanced methane production. (C) 2013 Elsevier Ltd. All rights reserved.11sciescopu

Effects of the ratio of carbon to nitrogen concentration on lipid production by bacterial consortium of sewage sludge using food wastewater as a carbon source

Food wastewater (FWW) and sewage sludge (SS) were used to control the C:N ratio in cultures as a method to increase lipid production by microbial species in SS. FWW and SS were mixed in volumetric ratios (FWW: SS) of 5: 0 (F5), 4: 1 (F4), or 3: 2 (F3). Compared to raw SS, total lipid content production was increased by 263% in F5, 142% in F4, and 111% in F3. These results were caused by increases in the concentrations of triglycerides (TAGs) during lipid enhancement. The fatty acid methyl ester content of TAGs (wt% of extract) was 25.3 in F5, 20.2 in F4 and 13.25 in F3; these were significant improvements over biodiesel production using raw SS. C16:0 fatty acid was mostly converted to C18:1 fatty acid; this is an important result because the proportion of C18:1 strongly influences the quality of biodiesel. This is the first effort to produce biodiesel using FWW instead of synthetic medium as a carbon source. Hence, this study provides a useful solution for treating organic wastes (SS and FWW) simultaneously; this strategy may be an economically viable method for producing biodiesel from organic wastes.11sciescopuskc

Combined mesophilic anaerobic and thermophilic aerobic digestion process for high-strength food wastewater to increase removal ficiency and reduce sludge discharge

In this study, a process that combines the mesophilic anaerobic digestion (MAD) process with thermophilic aerobic digestion (TAD) for high-strength food wastewater (FWW) treatment was developed to examine the removal of organic matter and methane production. All effluent discharged from the MAD process was separated into solid and liquid portions. The liquid part was discarded and the sludge part was passed to the TAD process for further degradation. Then, the digested sludge from the TAD process was recycled back to the MAD unit to achieve low sludge discharge from the combined process. The reactor combination was operated in two phases: during Phase I, 40 d of total hydraulic retention time (HRT) was applied; during Phase II, 20 d was applied. HRT of the TAD process was fixed at 5 d. For a comparison, a control process (single-stage MAD) was operated with the same HRTs of the combined process. Our results indicated that the combined process showed over 90% total solids, volatile solids and chemical oxygen demand removal efficiencies. In addition, the combined process showed a significantly higher methane production rate than that of the control process. Consequently, the experimental data demonstrated that the combined MAD-TAD process was successfully employed for high-strength FWW treatment with highly efficient organic matter reduction and methane production.11sciescopu

An innovative sewage sludge reduction by using a combined mesophilic anaerobic and thermophilic aerobic process with thermal-alkaline treatment and sludge recirculation

Lab-scale High Efficiency Digestion (HED) systems containing a Mesophilic Anaerobic Reactor (MAR), Thermophilic Aerobic Reactor (TAR), liquid/solid separation unit, and thermal-alkaline treatment were developed to evaluate the efficiencies of sludge reduction and methane production. The HED process was divided into three phases to examine the influence of sludge pretreatment and pretreated sludge recirculation using TCOD and VSS reduction, COD solubilization, and methane production. The VSS removal with a solid/liquid separation unit, sludge recirculation, and thermal-alkaline treatment drastically increased up to 95% compared to the feed concentration. In addition, the results of COD solubilization and VSS/TSS showed that the solubilization of cells and organic matters by the thermal-alkaline treatment was highly increased, which was also consistent with the SEM images. In particular, the methane production rate increased 24-fold when the feed sludge and recirculated sludge were pretreated together. Collectively, the HED experiments performed with sludge recirculation and thermal-alkaline treatment demonstrated that the HED systems can be successfully employed for highly efficient sewage sludge reduction and methane gas production. (C) 2013 Elsevier Ltd. All rights reserved.11sciescopu

Influence of thermophilic aerobic digestion as a sludge pre-treatment and solids retention time of mesophilic anaerobic digestion on the methane production, sludge digestion and microbial communities in a sequential digestion process

In this study, the changes in sludge reduction, methane production and microbial community structures in a process involving two-stage thermophilic aerobic digestion (TAD) and mesophilic anaerobic digestion (MAD) under different solid retention times (SRTs) between 10 and 40 days were investigated. The TAD reactor (R-TAD) was operated with a 1-day SRT and the MAD reactor (R-MAD) was operated at three different SRTs: 39, 19 and 9 days. For a comparison, control MAD (R-CONTROL) was operated at three different SRTs of 40, 20 and 10 days. Our results reveal that the sequential TAD-MAD process has about 42% higher methane production rate (MPR) and 15% higher TCOD removal than those of R-CONTROL, when the SRT decreased from 40 to 20 days. Denaturing gradient gel electrophoresis (DGGE) and real-time PCR results indicate that R-MAD maintained a more diverse bacteria and archaea population compared to R-CONTROL, due to the application of the biological TAD pre-treatment process. In R-TAD, Ureibacillus thermophiles and Bacterium thermus were the major contributors to the increase in soluble organic matter. In contrast, Methanosaeta concilii, a strictly aceticlastic methanogen, showed the highest population during the operation of overall SRTs in R-MAD. Interestingly, as the SRT decreased to 20 days, syntrophic VFA oxidizing bacteria, Clostridium ultunense sp., and a hydrogenotrophic methanogen, Methanobacterium beijingense were detected in R-MAD and R-CONTROL. Meanwhile, the proportion of archaea to total microbe in R-MAD and R-CONTROL shows highest values of 10.5 and 6.5% at 20-d SRT operation, respectively. Collectively, these results demonstrate that the increased COD removal and methane production at different SRTs in RmAD might be attributed to the increased synergism among microbial species by improving the hydrolysis of the rate limiting step in sludge with the help of the biological TAD pre-treatment. (C) 2013 Elsevier Ltd. All rights reserved.11sciescopu

Effect of increased load of high-strength food wastewater in thermophilic and mesophilic anaerobic co-digestion of waste activated sludge on bacterial community structure

In recent years, anaerobic co-digestion (AcoD) has been widely used to improve reactor performance, especially methane production. In this study, we applied two different operating temperatures (thermophilic and mesophilic) and gradually increased the load of food wastewater (FWW) to investigate the bacterial communities during the AcoD of waste activated sludge (WAS) and FWW. As the load of FWW was increased, methane production rate (MPR; L CH4/Ld) and methane content (%) in both Thermophilic AcoD (TAcoD) and Mesophilic AcoD (MAcoD) increased significantly; the highest MPR and methane content in TAcoD (1.423 L CH4/L d and 68.24%) and MAcoD (1.233 L CH4/L d and 65.21%) were observed when the FWW mixing ratio was 75%. However, MPR and methane yield in both reactors decreased markedly and methane production in TAcoD ceased completely when only FWW was fed into the reactor, resulting from acidification of the reactor caused by accumulation of organic acids. Pyrosequencing analysis revealed a decrease in bacterial diversity in TAcoD and a markedly different composition of bacterial communities between TAcoD and MAcoD with an increase in FWW load. For example, Bacterial members belonging to two genera Petrotoga (assigned to phylum Thermotogae) and Petrimonas (assigned to phylum Bacteroidetes) became dominant in TAcoD and MAcoD with an increase in FWW load, respectively. In addition, quantitative real-time PCR (qPCR) results showed higher bacterial and archaeal populations (expressed as 16S rRNA gene concentration) in TAcoD than MAcoD with an increase in FWW load and showed maximum population when the FWW mixing ratio was 75% in both reactors. Collectively, this study demonstrated the dynamics of key bacterial communities in TAcoD and MAcoD, which were highly affected by the load of FWW. (C) 2016 Published by Elsevier Ltd.11sciescopu

Enhanced Adsorption Removal of Pb(II) and Cr(III) by Using Nickel Ferrite-Reduced Graphene Oxide Nanocomposite

The heavy metals, such as Pb(II) and radioisotope Cr(III), in aqueous solutions are toxic even at trace levels and have caused adverse health impacts on human beings. Hence the removal of these heavy metals from the aqueous environment is of the utmost importance to protect biodiversity, hydrosphere ecosystems, and human beings. In this study, the reduced graphene oxide based inverse spinel nickel ferrite (rGONF) nanocomposite has been prepared and was utilized for the removal of Pb(II) and Cr(III) from aqueous solutions. The prepared rGONF has been confirmed by X-ray photoelectron (XPS) and Raman spectroscopy. The surface characteristics of rGONF were measured by scanning electron microscopy (SEM), High-Resolution Transmission Electron Microscope (HR-TEM), and Brunauer-Emmett-Teller (BET) surface analysis. The average particle size of rGONF was found to be 32.0 ± 2.0 nm. The surface site density for the specific surface area (Ns) of rGONF was found to be 0.00238 mol·g−1, which was higher than that of the graphene oxide (GO) and NiFe2O4, which was expected. The prepared rGONF has been successfully applied for the removal of Pb(II) and Cr(III) by batch mode. The batch adsorption studies concluded that the adsorption of Pb(II) and Cr(III) onto rGONF was rapid and the adsorption percentage was more than 99% for both metal ions. The adsorption isotherm results found that the adsorptive removal of both metal ions onto rGONF occurred through monolayer adsorption on a homogeneous surface of rGONF. The pH-edge adsorption results suggest the adsorption occurs through an inner-sphere surface complex, which is proved by 2-pKa-diffusion model fitting, where the pH-edge adsorption data was well fitted. The adsorption of metal ions increased with increasing temperature. The overall obtained results demonstrated that the rGONF was an effective adsorbent for Pb(II) and Cr(III) removal from wastewater