Electrochemical disinfection and removal of ammonia nitrogen for the reclamation of wastewater treatment plant effluent.

Residual ammonia and pathogenic microorganisms restrict the reclamation and reuse of wastewater treatment plant (WWTP) effluent. An electrochemical system was developed for the simultaneous removal of ammonia and disinfection of actual WWTP effluent. The performance of the electrochemical process on synthetic wastewater at different chloride ion concentrations was also investigated. Results demonstrated that the optimal chloride concentration for ammonia and Escherichia coli (E. coli) removal was 250 mg/L. Successful disinfection of E. coli in actual effluent was achieved at 0.072 Ah/L, but the inverse S-type inactivation curve indicated that there was a competitive consumption of strong oxidants and chloramines working as another disinfectant. A higher electric charge (0.58 Ah/L) was required to simultaneously reduce E. coli and ammonia to levels that meet the reclamation requirements for WWTP effluent. At this electric charge, no trihalomethane, chlorate, or perchlorate in the system was observed, indicating the biological safety of this process. These results demonstrate the potential of this electrochemical process as a tertiary wastewater treatment process for WWTP effluent reclamation purposes.

Ammonium nitrogen removal from wastewater with a three-dimensional electrochemical oxidation system.

Ammonium-containing wastewater could cause the promotion of eutrophication and a hindrance to the disinfection of water supplies. In this study, the feasibility of removing low-concentration ammonium nitrogen from synthetic and real wastewater by electrochemical oxidation was investigated. Using laboratory-scale electrochemical systems, the effects of chloride concentration, current density, anode materials, cathode materials, electrode gap, initial ammonium concentration and three-dimensional particles on the removal of ammonium nitrogen and current efficiency (CE) were evaluated. Ammonium nitrogen removal was mainly dependent upon anode materials and current density. The performance of two- and three-dimensional electrochemical oxidation systems was comparatively discussed. Both particle electrodes could enhance ammonium nitrogen removal and increase CE. However, the mechanism of the process seemed to be different. Moreover, the interaction of zeolites adsorption and electrochemical oxidation on the anode in a three-dimensional system could favor the regeneration of zeolites. Surface morphology of the used Ru-Ir-Sn/Ti anode revealed its longer working life of electrocatalysis. The result of ammonium degradation for a real wastewater treatment plant effluent showed the degradation rates in a three-dimensional system increased by 1.4 times those in a two-dimensional system.

Fractional, biodegradable and spectral characteristics of extracted and fractionated sludge extracellular polymeric substances.

Correlation between fractional, biodegradable and spectral characteristics of sludge extracellular polymeric substances (EPS) by different protocols has not been well established. This work extracted sludge EPS using alkaline extractants (NH4OH and formaldehyde + NaOH) and physical protocols (ultrasonication, heating at 80 °C or cation exchange resin (CER)) and then fractionated the extracts using XAD-8/XAD-4 resins. The alkaline extractants yielded more sludge EPS than the physical protocols. However, the physical protocols extracted principally the hydrophilic components which were readily biodegradable by microorganisms. The alkaline extractants dissolved additional humic-like substances from sludge solids which were refractory in nature. Different extraction protocols preferably extracted EPS with distinct fractional, biodegradable and spectral characteristics which could be applied in specific usages.

Extracellular biological organic matters in sewage sludge during mesophilic digestion at reduced hydraulic retention time.

To operate an anaerobic digester at low hydraulic retention time (HRT) is welcome in practice. This study characterized the extracellular biological organic matter (EBOM) and supernatant organics for a sewage sludge digested in a lab-scale mesophilic digester (5 l) running at an HRT of 20, 15 or 10 d. The hydrophilic and hydrophobic acid fractions were the principal components in the sludge EBOM. The hydrolysis rates for hydrophobic acid fraction related EBOM at 10 d HRT and that of hydrophilic fraction related proteins in supernatant at 20 d HRT limited the anaerobic processes. Improved hydrolysis of soluble hydrophilic fraction assisted improving digester performance at 20 d HRT. To shorten digestion HRT, efficiency of hydrophobic acid fraction hydrolysis has to be practiced.

Characterization of dissolved organic matter during landfill leachate treatment by sequencing batch reactor, aeration corrosive cell-Fenton, and granular activated carbon in series.

Landfill leachate is generally characterized as a complex recalcitrant wastewater containing high concentration of dissolved organic matter (DOM). A combination of sequencing batch reactor (SBR)+aeration corrosive cell-Fenton (ACF)+granular activated carbon (GAC) adsorption in series was proposed for the purpose of removing pollutants in the leachate. Fractionation was also performed to investigate the composition changes and characteristics of the leachate DOM in each treatment process. Experimental results showed that organic matter, in terms of chemical oxygen demand (COD), 5-day biological oxygen demand (BOD(5)), and dissolved organic carbon (DOC), was reduced by 97.2%, 99.1%, and 98.7%, respectively. To differentiate the DOM portions, leachates were separated into five fractions by XAD-8 and XAD-4 resins: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). The predominant fraction in the raw leachate was HPO-A (36% of DOC), while the dominant fraction in the final effluent was HPI (53% of DOC). Accordingly, macromolecules were degraded to simpler ones in a relatively narrow range below 1000 Da. Spectral and chromatographic analyses also showed that most humic-like substances in all fractions were effectively removed during the treatments and led to a simultaneous decrease in aromaticity.

Reduction of trihalomethane precursors of dissolved organic matter in the secondary effluent by advanced treatment processes.

Wastewater effluent collected from the Wenchang Wastewater Treatment Plant (Harbin, China) was used as source water for advanced treatment and reclamation. Since dissolved organic matter (DOM) in the secondary effluent contains a high concentration of trihalomethanes (THMs) precursors, several processes of advanced treatments including granular activated carbon (GAC) adsorption, sand column biodegradation, horizontal subsurface flow wetland (HSFW) treatment, laboratory-scale soil aquifer treatment (SAT) and GAC+SAT were used in this study to compare and differentiate the removal mechanisms of DOM. DOM in the secondary effluent and the treated effluents was fractionated into five classes using XAD resins: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). Results showed that HPO-A and HPI were two main fractions of the DOM in the secondary effluent, accounting for 30.0% and 45.5% of the bulk DOM, respectively. HPO-A exhibited higher trihalomethane formation potential (THMFP) and specific THMFP (STHMFP) than HPI during the chlorination process. The order of the dissolved organic carbon (DOC) removal with respect to different advanced treatments was observed to be GAC+SAT>SAT>GAC>sand column>HSFW. As for the DOM removal mechanisms, the advanced treatment processes of GAC adsorption, SAT and GAC+SAT tended to adsorb more HPO-A, HPO-N and TPI-A and could reduce the aromaticity of those DOM fractions efficiently. Correspondingly, the advanced treatment processes of sand column, SAT, HSFW and GAC+SAT removed more HPI and TPI-N through biodegradation and each of the DOM fractions had an increased aromaticity. The removal order of the THMs precursor by the advanced treatment processes was GAC+SAT>GAC>SAT>sand column>HSFW. The adsorption reduced the STHMFP of the DOM fractions effectively, whereas the biodegradation mechanism of the treatments (sand column, SAT, GAC+SAT and HSFW) showed a converse trend. Moreover, the THMFP and STHMFP of the DOM in the HSFW effluent were obviously affected by the DOM derived from the leaves and roots.

Behavior and characteristics of dissolved organic matter during column studies of soil aquifer treatment.

Soil column experiments were performed to investigate the behavior and characteristics of dissolved organic matter (DOM) during soil aquifer treatment (SAT), and to differentiate among the mechanisms responsible for the changes in the structural and functional properties of DOM during SAT. To determine the biological transformation of DOM, biodegradability tests using a biodegradation-column system were conducted. DOM was fractionated using XAD resins into 5 fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Dissolved organic carbon (DOC) was removed by 70% during SAT, and the sorption and anaerobic biodegradation in SAT led to a DOC reduction of 27.4%. The significant changes in fluorescence properties of DOM were observed during SAT. However, the sorption and anaerobic biodegradation in SAT seemed to have no significant effect on the chemical structure of fluorescing constituents in DOM. The DOM fractions exhibited different changes in Fourier-transform infrared (FT-IR) spectra characteristics during SAT. Biodegradation resulted in the enrichment of aromatic structures and the decreased content of the oxygen-containing functional groups, such as CO and C-O, in DOM. On the other hand, the production of C-O and amide-2 functional groups occurred as a result of the sorption combined with anaerobic biodegradation in SAT.

[Effect of chlorination on the structure of dissolved organic matters in secondary effluent].

Dissolved organic matter in the secondary effluent from the W wastewater treatment plant (Harbin) was fractionated using XAD resins into five fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The distribution, trihalomethane formation potential (THMFP), UV-Vis and FTIR spectra of organic fractions in the secondary effluent were examined. XAD fractionation results showed that HPO-A and HPI dominated in the secondary effluent, collectively accounting for about 70.8%. HPO-A was the main precursors for THMFP following chlorination. HPO-A had the highest specific THMFP (STHMFP) and averaged 232.9 microg/mg. The STHMFP of HPO-N, TPI-A, TPI-N and HPI ranged from 100 microg/mg to 125 microg/mg. Chlorination resulted in increased UV-Vis absorbance for TPI-N and decreased UV-Vis absorbance for HPO-A, HPO-N, TPI-A and HPI. After chlorination, O--H, C=C and aromatic ring were found to decrease while C--O was observed to increase for HPO-A, HPO-N, TPI-A and TPI-N. In addition,C=O and C--Cl were found to occur as by-products from the chlorination reaction.

Effect of bromide ion on isolated fractions of dissolved organic matter in secondary effluent during chlorination.

The role of bromide ion in the trihalomethane (THM) formation and structure of dissolved organic matter (DOM) during chlorination of the secondary effluent taken from the Wenchang Wastewater Treatment Plant (Harbin, China) was investigated. DOM was fractionated using XAD resins into five fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The patterns of individual THM species with increased bromide concentrations were similar for all DOM fractions. The THM speciation as well as halogen fraction for these five fractions followed similar trends with the Br(-)/Cl(2) ratio. Chlorination resulted in decreased ultraviolet (UV) absorbance across wavelengths from 250 to 280 nm for DOM fractions whether bromide ions existed or not, and bromide addition led to lower differential UV absorbance values. Fourier-transform infrared (FT-IR) results indicated that chlorination, whether bromide ions existed or not, resulted in the near elimination of aromatic CH and amide peaks, increased CO absorption intensity and occurrence of CO and CCl peaks for HPO-A, HPO-N, TPI-A and TPI-N. Furthermore, bromide addition in chlorination led to the occurrence of CBr peak for all four fractions.