Photodegradation of Pb-3,4-dihydroxybenzoic acid complex under UV light illumination

The degradation of 3,4-dihydroxybenzoic acid (3,4-DHBA) in the presence and absence of Pb(2+) under UV illumination was studied. Addition of Pb(2+) caused the formation of precipitate during photoreaction when the solution pH was higher than 6. The presence of Pb(2+) remarkably inhibited the degradation of 3,4-DHBA and its photodegradation intermediates, while complexation of 3,4-DHBA and its photodegradation intermediates with Pb(2+) decreased the free Pb(2+) in aqueous solutions. Molecular oxygen played an important role in photodegradation of 3,4-DHBA in the presence of Pb(2+). UV-Vis spectroscopy was used to investigate the interaction between Pb(2+) and 3,4-DHBA at different pH conditions, and FT-IR was used to characterize the precipitate formed during photoreaction. The mineralization of 3,4-DHBA was investigate by total organic carbon analysis.     

Coagulation of NOM: linking character to treatment.

The paper presents an overview and discussion on the link between natural organic matter (NOM) character and its treatability by coagulation. Trials were conducted on a series of bench scale and pilot plant trials on three source waters: two from UK moorland catchments and one from a US snow melt source. Overall the work demonstrates the importance of the polarity balance and the charge density of the NOM contained within the source water. The hydrophobic content controls the coagulant demand such that variation in the demand between sources or sampling periods can be accounted for by changes in the hydrophobic content and its charge density. The raw water hydrophilic content, and specifically the nonacid fraction, provides a useful indicator of the achievable residual. Analysis of coagulation performance revealed a clear relationship between zeta potential and residual DOC. For each source an operational zeta potential range exists within which the residual concentration is optimal. Comparison of the ranges achieved during each trial demonstrated that a communal range between -10 and +3 mV exist for all waters thus providing a useful guide range for operational control.     

光照对固定化菌藻反应器脱氮除磷效率的影响

采用气升式反应器对日光灯光暗比、日光灯光源和二极管光源在固定化菌藻共生系统去除氮磷的作用进行试验研究。结果表明:延长光照时间有利于该系统对NH4+-N、PO43--P的去除,采用日光灯光源去除效果优于采用二极管光源。     

Pathogen removal efficiency from UASB + BF effluent using conventional and UV post-treatment systems.

The aim of this study was to verify the efficiency of removal of microorganisms in effluents of a Wastewater Treatment Plant (WWTP) comprising an association of a UASB reactor followed by three submerged aerated biofilters (BAF) and one tertiary filter. The WWTP designed to treat domestic wastewater from a population of 1,000 inhabitants showed high removal efficiency for organic matter and suspended solids. Helminth eggs were also efficiently removed from the tertiary effluent and were found in the sludge from the UASB reactor; however, removal of bacteria in this system was very low. To enhance the efficiency of the system, the effluent from tertiary filters was submitted to UV disinfection in a real scale reactor. Our results showed that UV irradiation was very effective at lowering the concentrations of E. coli, thermotolerant coliforms and coliphages to acceptable levels for agricultural reuse. Salmonella spp. and helminth eggs were seeded into the tertiary effluent before passing through the UV reactor. Salmonella was not found in the final effluent, but helminth eggs were not completely inactivated by UV irradiation and viable eggs were detected after 28 d of incubation.     

UV/H_2O_2/微曝气降解三氯乙酸的试验研究

UV/H2O2/微曝气工艺是在常规UV/H1O2基础上发展起来的.试验表明在紫外光强1 048.7μW/cm2,H20z投加量为40 mg/L,三氯乙酸(TCAA)初始浓度约为110μg/L的情况下,120 min后该工艺对TCAA的去除达到90%以上.工艺效果受UV光强,H2O2投加量,TCAA初始浓度和pH的影响.其他条件一定时,随着UV光强和H2O2投加量的增大,TCAA去除率增加.然而H2O2投加量超过40 mg/L后,去除效果增加缓慢.对不同初始浓度,103.5μg/L时去除率最高,而后浓度增加,去除率下降.TCAA中性或弱酸性pH条件下更有利于降解.     

有机滤光剂在水环境中的污染现状及去除技术

新兴污染物有机滤光剂对水生生态环境和人类健康造成威胁,对其在水环境中的污染调查及控制已成为研究热点。通过对现有研究的分析,归纳了当前国内外水环境中有机滤光剂的污染现状,综述了有机滤光剂的主要去除方法,并展望了该领域进一步的研究重点与方向。     

Helminth eggs removal by microscreening for water reclamation and reuse.

Irrigation with reclaimed water is becoming a practical alternative to conventional irrigation in semi-arid areas of the Mediterranean like Spain, but it requires a reliable treatment process to provide a safe water supply. Helminth eggs are one of the main concerns for the safe use of reclaimed water, as they can survive adverse environmental conditions and they are highly infective. Spanish water quality criteria and International guidelines set a limit of 0.1 eggs/l for water uses with unrestricted human exposure. Two microscreening processes have been tested to determine their potential for helminth eggs removal, after a conventional physic-chemical reclamation process. Hydrotech Drum and Discfilters, provided with 10 microm pore size filter cloth, were tested to determine their efficiency for helminth eggs straining. An experimental test was conducted using 20 microm spherical latex particles, as surrogates for helminth eggs, to test the removal efficiency of a small full-scale drumfilter. In a subsequent laboratory test, actual Trichuris suis eggs were strained using a 10 microm pore size filter cloth from a discfilter. Results from both tests indicate that drum and discfilters are able to achieve 99% removal efficiency for spherical latex particles and a complete removal for helminth eggs in reclaimed water.     

Technical and sanitary aspects of wastewater disinfection by UV irradiation for landscape irrigation.

Water reuse for landscape irrigation requires the production of high quality virus-free effluents to minimize risk for human health. In order to establish the relevance of MS2 phages as an appropriate biodosimeter for UV design, a pilot plant study has been carried out with different types of wastewater effluents. The two pilot systems tested (low-pressure high output and medium-pressure UV units) were able to achieve 4 and 5 log MS2 reduction in tertiary filtered effluent at high calculated UV doses of 170 _ 10 and 300 mJ/cm2, respectively. UV disinfection was extremely efficient for MS2 inactivation in high quality effluents after reverse osmosis: detention times as low as one second and UV dose of 40 mJ/cm2 were sufficient to reach 5 log inactivation of MS2. UV irradiation also produced rapid inactivation of human pathogens such as poliovirus type 1 and indigenous enteroviruses at UV doses up to 3 times lower that those for MS2 disinfection. It was concluded that accurate UV unit design for a given type of wastewater could be ensured by pilot tests using laboratory-propagated MS2 as biodosimeter and collimated-beam tests as the calibration-check.     

UV/H2O2和UV/TiO2/H2O2去除水中微量硝基苯的比较研究

研究比较了UV/H2O2和UV/TiO2/H2O2对水中微量硝基苯的降解效果,并考察了水中常见HCO-3和腐殖酸对硝基苯降解的影响.结果表明,薄膜状TiO2的存在对UV/H2O2降解硝基苯有显著的促进作用,在最佳H2O2投加量2.1 mg/L时,UV/TiO2/H2O2的反应速率常数比UV/H2O2高32.8%;2 min内UV/TiO2/H2O2对硝基苯的去除率达到80%以上.HCO-3和腐殖酸对硝基苯降解有很强的抑制作用,HCO-3和腐殖酸浓度分别为2 mmol/L和3.2 mg/L时,UV/TiO2/H2O2对硝基苯的反应速率常数分别下降84.6%和92.2%.     

Degradation of the endocrine disruptor carbofuran by UV, O3 and O3/UV.

The photodegradation of a carbamate insecticide, Carbofuran (CBF), which has been recognised as a potential endocrine disrupting chemical, was studied via different wastewater treatment processes. This study has shown the efficiency of advanced oxidation process, AOP (UV/O3) than those of the direct UV photolysis and ozonation process, by completely removing 0.2 mM CBF and achieving 24% mineralisation within 30min. The initial decay of CBF by UV/O3 accelerated from 0.05 to 0.16 min(-1) as the initial pH increasing from 3.0 to 11.3. The pH-dependency of CBF has also been shown in both ozonation and UV/O3 process. A linear relationship could be found for the latter process in all pH, while for the former process, two stages of reactions (steady and accelerating) were found in the acidic and alkaline pH condition, respectively.     

Photocatalytic degradation of toluene by platinized titanium dioxide photocatalysts.

A photoreactor has been set up to study the photodegradation of volatile organic compound (VOC) in situ. In the reactor, TiO2 and Pt/TiO2 photocatalysts were immobilized on to UV-transparent quartz support. Scanning electron microscope (SEM) studies and Brunauer-Emmett-Teller (BET) surface area measurements revealed that the quartz fiber support was mostly coated with catalyst with a total surface area of 4.0 +/- 0.3 m2/g. The photocatalytic activity of the photocatalysts was evaluated for the photodegradation of 160 ppm toluene-laden air. It was found that 50-70% of toluene was degraded within the first 5 min of UV illumination. Both TiO2 and Pt/TiO2 photocatalysts suffered from deactivation after 18 hours of continuous operation, and the photocatalysts' activity was significantly reduced. However, platinization doubled the photocatalyst life and delayed the onset of de-activation. The presence of moisture was found to shift the onset of catalyst de-activation to an earlier time. It is concluded that the de-activation of the photocatalyst was due to the accumulation of intermediates on the photocatalysts surface preventing the toluene being adsorbed on the photocatalyst surface for degradation.     

UV disinfection of wastewater effluents for unrestricted irrigation.

Wastewater reuse in arid regions is important for the production of a water resource to be utilised for non-potable purposes and to prevent the environmental transmission of disease-causing agents. This study was conducted to evaluate the effect of water quality on the comparative disinfection efficiency of viruses, bacteria and spores by UV irradiation. Furthermore, the microbial quality of effluent produced by coagulation, high rate filtration (HRF) and either UV irradiation or chlorination was determined. Using low pressure collimated beam, a UV dose of 80 mWs/cm2 was needed to achieve a 3-log10 inactivation of either rotavirus SA-11 or coliphage MS2, whereas over 5-log10 inactivation of E. coli was reached with a dose of only 20 mWs/cm2. B. subtilis inactivation was found to be linear up to a dose of 40 mWs/cm2 and then a tailing up to a UV dose of 120 mWs/cm2 was observed. It is worth noting that effluent turbidity of < 5 NTU did not influence the inactivation efficiency of UV irradiation. Operation of a pilot plant to treat secondary effluent by coagulation, HRF and UV disinfection at a UV dose of 80 mWs/cm2 resulted in the production of high quality effluent in compliance with the Israel standards for unrestricted irrigation (< 10 CFU/100 mL faecal coliform and turbidity of < 5 NTU). Sulphite reducing clostridia (SRC) were found to be more resistant than coliphages and F coliform for UV irradiation. The results of this study indicated that UV disinfection is suitable for the production of effluents for unrestricted irrigation of food crops.     

Hydrogen sulphide removal by activated sludge diffusion.

Odours from wastewater treatment plants comprise a mixture of various gases, of which hydrogen sulphide (H2S) is the main constituent. Microorganisms commonly found in wastewater can degrade sulphurous compounds. Therefore, the use of activated sludge (AS) for odour control offers an alternative to traditional waste gas treatment processes, such as biofilters, bioscrubbers and biotrickling filters, both in practical terms (use of existing facilities) and economically (minimal capital cost). The performance of AS diffusion as a bioscrubber for removing H2S at concentrations at 25, 75 and 150 ppmv was evaluated. Pilot-scale trials were undertaken using parallel 60-L aeration tanks and 20-L clarifier reactors at the Bedford Sewage Treatment Works, Carington, UK. Olfactometry measurements were also carried out to determine whether there was any increase in odour concentration owing to H2S diffusion. Hydrogen sulphide removal rates of 100% were obtained, with no noticeable increase in odour concentration throughout the trials as measured by olfactometry. Odour concentration was highest at the beginning of the trials and lowest during the high H2S dosing period, with similar values being obtained for test and control. It was concluded that AS diffusion is an effective bioscrubber for the removal of H2S odour.     

AOPs with ozone and UV radiation in drinking water: contaminants removal and effects on disinfection byproducts formation.

In this study, the advanced oxidation with ozone and UV radiation (with two low pressure UV lamps, at 254 and 185 nm wavelength) were experimented on a surface water in order to study the removal of two odorous compounds (geosmin and 2-methylisoborneol) and a pesticide (metolachlor), the influence on organic compounds (UV absorbance and THM precursors) and bromate formation. Different batch tests were performed with ozone concentration up to 10 mg/L, UV dose up to 14,000 J/m2 and a maximum contact time of 10 minutes. The main results show that metolachlor can be efficiently removed with ozone alone while for geosmin and MIB a complete removal can be obtained with the advanced oxidation of ozone (with concentration of 1.5-3 mg/L and contact time of 2-3 minutes) with UV radiation (with doses of 5,000-6,000 J/m2). As concerns the influence on the organic precursors, all the experimented processes show a medium removal of about 20-40% for UV absorbance and 15-30% for THMFP (trihalomethanes formation potential). As concerns bromate formation, the advanced oxidation of ozone/UV 254 nm shows a bromate formation that is about 40% lower with respect to conventional oxidation with ozone.     

Characterization of micro-flocs of NOM coagulated by PACl, alum and polysilicate-iron in terms of molecular weight and floc size.

Micro-flocs of NOM coagulated by polyaluminium chloride (PACl), alum and polysilicate-iron (PSI) were characterized by flocs size, HPSEC-based molecular weight and the captured content of coagulants-based aluminium and iron. Changes in floc composition with respect to the mass ratios of captured NOM to Al and Fe were examined. Lowering water pH to optimum levels was found to be capable of removing small NOM constituents that are generally difficult to be precipitated at neutral pH levels. For PACl and PSI, the distribution of micro flocs (0.1-5.0 microm) reached steady stage after rapid mixing for 30 seconds, with NOM being found existent within the non-coagulated fraction (d<0.1 microm) and the coagulated fraction with floc sizes above 5.0 microm (d >5.0 microm). For alum, however, the existence of NOM inside intermediate floc fractions of d = 0.1-1.0 microm, 1.0-3.0microm and 3.0-5.0 microm was confirmed.     

Arsenic removal by iron and manganese coated sand.

In this study, as a promising technique for the treatment of both As(III) and As(V) at the same time in a single reactor, a column reactor containing both manganese-coated sand (MCS) and iron-coated sand (ICS), at different configuration of MCS and ICS, was used to treat wastewater contaminated with As(III). Prior to column experiments, batch experiments for the adsorption of As(V) by ICS were performed with variation of solution pH, ionic strength and types of background ions to investigate the effect of these parameters on the As(V) adsorption behaviour. As(V) adsorption onto ICS was quite similar with the variation of ionic strength by using NaNO3 as a background ion as well as in the presence of different types of background ions except phosphate. The adsorption curves shifted to the lower pH region with the increase of the initial arsenic concentration due to the finite number of adsorption sites on the ICS. For model prediction on the adsorption of As(V) onto ICS, the MINEQL program employing an inner-sphere complexation and a diffuse layer model was used. Model predictions generally agreed well with experimental results. From the column test, column system packed with equal ratio of MCS and ICS was identified as the best system due to a promising oxidation efficiency of As(III) to As(V) by MCS and adsorption of As(V) by both MCS and ICS.     

Factors affecting nitrogen removal by nitritation/denitritation.

Nitrogen removal from wastewater with high nitrogen concentration and low COD/N ratio via nitrite is advantageous. The specific character of the sludge liquor enables the application of such a method. The factors affecting process efficiency were studied. From the factors followed pH, NH4+/NH3 and NO2-/HNO2 concentration and distribution seem to be most important, using sequencing batch reactor technology and treating wastewater with high NH4+ concentration (above 1 g/l). The efficient oxidation of N-NH4+ to nitrite was achieved at a minimal nitrate production. Primary sludge was used as an internal source of substrate for the denitritation because of the organic substrate deficiency of the sludge liquor. The denitritation can be controlled by dosing of the primary sludge and can be complete. There are two operational alternatives of sludge liquor pretreatment: without pH control--lower operational costs and N-removal up to 65% and with pH control--higher operational costs and N-removal close to complete.     

Re-use of winery wastewaters for biological nutrient removal.

The aim of this study was to evaluate the feasibility of the re-use of the winery wastewater to enhance the biological nutrient removal (BNR) process. In batch experiments it was observed that the addition of winery wastewater mainly enhanced the nitrogen removal process because of the high denitrification potential (DNP), of about 130 mg N/g COD, of the contained substrates. This value is very similar to that obtained by using pure organic substrates such as acetate. The addition of winery wastewater did not significantly affect either phosphorus or COD removal processes. Based on the experimental results obtained, the optimum dosage to remove each mg of N-NO3 was determined, being a value of 6.7 mg COD/mg N-NO3. Because of the good properties of the winery wastewater to enhance the nitrogen removal, the viability of its continuous addition in an activated sludge pilot-scale plant for BNR was studied. Dosing the winery wastewater to the pilot plant a significant increase in the nitrogen removal was detected, from 58 to 75%. The COD removal was slightly increased, from 89 to 95%, and the phosphorus removal remained constant.