Catalyzed UV oxidation of organic pollutants in biologically treated wastewater effluents

Treatment of hospital laundry wastewater by UV/H2O2 process

Hospitals consume a large volume of water to carry out their activities and, hence, generate a large volume of effluent that is commonly discharged into the local sewage system without any treatment. Among the various sectors of healthcare facilities, the laundry is responsible for the majority of water consumption and generates a highly complex effluent. Although several advanced oxidation processes (AOPs) are currently under investigation on the degradation of a variety of contaminants, few of them are based on real wastewater samples. In this paper, the UV/H₂O₂ AOP was evaluated on the treatment of a hospital laundry wastewater, after the application of a physicochemical pretreatment composed of coagulation-flocculation and anthracite filtration. For the UV/H₂O₂ process, a photoreactor equipped with a low-pressure UV-C lamp was used and the effects of initial pH and [H₂O₂]/chemical oxygen demand (COD) ratio on COD removal were investigated through a randomized factorial block design that considered the batches of effluent as blocks. The results indicated that the initial pH had no significant effect on the COD removal, and the process was favored by the increase in [H₂O₂]/COD ratio. Color and turbidity were satisfactorily reduced after the application of the physicochemical pretreatment, and COD was completely removed by the UV/H₂O₂ process under suitable conditions. The results of this study show that the UV/H₂O₂ AOP is a promising candidate for hospital laundry wastewater treatment and should be explored to enable wastewater reuse in the washing process.

Comparative study on DBPs formation profiles of intermediate organics from hydroxyl radicals oxidation of microbial cells

This study assessed the characteristics of disinfection byproducts (DBPs) formation from intermediate organics during UV/H2O2 treatment of activated sludge and algae cells under various reaction conditions. The DBPs including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs) and haloacetonitriles (HANs) in UV/H2O2-treated and chlorinated water were measured. The results showed that both dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) increased during the initial stage of UV/H2O2 treatment due to the lysis of sludge and algae cells, which enhanced the formation of both C- and N-DBPs; however, both DOC and DON decreased after longer reaction times. During the UV/H2O2 treatments, THMs formation potential (THMFP) peaked earlier than did HAAs formation potential (HAAFP). This shows that the dissolved organics released from lysis of microbial cells in the early stages of oxidation favor the production of THMs over HAAs; however, HAAs precursors increased with the oxidation time. Chlorination with bromide increased the formation of THMs and HAAs but less HKs and HANs were produced. Comparisons of normalized DBP formation potential (DBPFP) of samples collected during UV/H2O2 treatments of four different types of organic matter showed that the highest DBPFP occurred in filtered treated wastewater effluent, followed by samples of activated sludge, filtered eutrophicated pond water, and samples of algae cells. With increasing oxidation time, the dominant DBP species shifted from THMs to HAAs in the samples of activated sludge and algae cells. The DBPFP tests also showed that more HAAs were formed in biologically treated wastewater effluent, while the eutrophicated source water produced more THMs.

The Analysis of a Microbial Community in the UV/O3-Anaerobic/Aerobic Integrated Process for Petrochemical Nanofiltration Concentrate (NFC) Treatment by 454-Pyrosequencing

In this study, high-throughput pyrosequencing was applied on the analysis of the microbial community of activated sludge and biofilm in a lab-scale UV/O₃- anaerobic/aerobic (A/O) integrated process for the treatment of petrochemical nanofiltration concentrate (NFC) wastewater. NFC is a type of saline wastewater with low biodegradability. From the anaerobic activated sludge (Sample A) and aerobic biofilm (Sample O), 59,748 and 51,231 valid sequence reads were obtained, respectively. The dominant phylotypes related to the metabolism of organic compounds, polycyclic aromatic hydrocarbon (PAH) biodegradation, assimilation of carbon from benzene, and the biodegradation of nitrogenous organic compounds were detected as genus Clostridium, genera Pseudomonas and Stenotrophomonas, class Betaproteobacteria, and genus Hyphomicrobium. Furthermore, the nitrite-oxidising bacteria Nitrospira, nitrite-reducing and sulphate-oxidising bacteria (NR-SRB) Thioalkalivibrio were also detected. In the last twenty operational days, the total Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal efficiencies on average were 64.93% and 62.06%, respectively. The removal efficiencies of ammonia nitrogen and Total Nitrogen (TN) on average were 90.51% and 75.11% during the entire treatment process.

Toxicity effects of nickel electroplating effluents treated by photoelectrooxidation in the industries of the Sinos River Basin

<p>The Sinos river Basin is an industrial region with many tanneries and electroplating plants in southern Brazil. The wastewater generated by electroplating contains high loads of salts and metals that have to be treated before discharge. After conventional treatment, this study applied an advanced oxidative process to degrade organic additives in the electroplating bright nickel baths effluent. Synthetic rinsing water was submitted to physical-chemical coagulation for nickel removal. The sample was submitted to ecotoxicity tests, and the effluent was treated by photoelectrooxidation (PEO). The effects of current density and treatment time were evaluated. The concentration of total organic carbon (TOC) was 38% lower. The toxicity tests of the effluent treated using PEO revealed that the organic additives were partially degraded and the concentration that is toxic for test organisms was reduced.</p>

Efficiency of the UV/H2O2 process for the disinfection of humic surface waters

The efficiency of the UV/H2O2 process for the disinfection of total coliforms and the prevention of bacterial regrowth in humic surface waters were investigated. Inactivation of total coliforms was determined in water samples containing various concentrations ranging from 0-10 mg/L dissolved organic carbon (DOC) of fulvic acid, which were exposed to various doses (68-681 mWs/cm2) of UV radiation in the presence of 0.125 mg/L and 3.000 mg/L of hydrogen peroxide. Disinfection efficiencies of the UV radiation and the UV/H2O2 processes were compared. The results of bacterial inactivation experiments showed that the performances of the UV and the UV/H2O2 (0.125) were comparable whereas the UV/H2O2 (3.000) process showed significant improvement in performance, especially, in highly humic waters. Inactivation coefficient appeared to be almost doubled by the addition of 3.000 mg/L hydrogen peroxide during the treatment of highly humic waters. In contradiction to significant regrowth which occurred in the single UV radiation treatment, residual bacteria following the UV/H2O2 (0.125) and the UV/H2O2 (3.000) treatments were completely inactivated during dark incubation indicating the elimination of possible bacterial regrowth.

Is semi-flocculation effective as pretreatment to ultrafiltration in wastewater treatment?

In this study, ferric chloride (FeCl(3)) flocculation was used as a pretreatment to ultrafiltration (UF) in treating synthetic wastewater containing synthetic organic matter (SOM). The effect of flocculant dose was studied in terms of organic removal and membrane flux decline. The UF with optimum dose of FeCl(3) (68 mg L(-1)) did not experience any flux decline during the whole operation of 6 h. The preflocculation with a smaller dose of 20 mg L(-1) of FeCl(3) led to a severe flux decline in the UF (more than 65% in 6 h). To understand the phenomenon of the flux decline of UF, the MW ranges of SOM removed by different doses of FeCl(3) and by the post treatment of UF were studied. Flocculation with at least 50 mg L(-1) of FeCl(3) dose was found to be necessary to avoid any significant flux decline and to obtain superior DOC removal.

Treatment of biorefractory organic compounds in wool scour effluent by hydroxyl radical oxidation

Wool scouring effluent that had been treated with chemical flocculation and aerobic biological treatment (Sirolan CFB effluent) was tertiary treated by hydroxyl radical oxidation to remove residual organic compounds. These compounds impart a high chemical oxygen demand of 500-3000 mg/L and dark colour. However, a H2O2/UV process was found to effectively treat the majority of residual compounds, with up to 75% COD, 85% total organic carbon, and 100% removal of colour (T(480 nm)) achieved. This was despite the effluent being strongly absorbing in the UV region, with a film thickness of 0.21 mm reducing T(254 nm) by 50%. Treatment was unaffected by pH over the range 3-9. H2O2/UV treatment increased the biodegradability of the effluent (5-day biochemical oxygen demand increased from < 10 to 86 mg/L), but a combined chemical and biological process did not increase maximum COD removal or overall process efficiency. The tertiary treated effluent had a final COD in the range 125-750 mg/L, equating to a total COD removal from raw wool scour effluent of approximately 97.5%. This degree of treatment is sufficient for discharge in many, but not all, circumstances.