Ozone micro-bubble disinfection method for wastewater reuse system.

Reuse of wastewater is regarded as one important way to deal with the world's shortage of potable water. The authors focused on a disinfection system using micro-bubbles and evaluated its capability for wastewater reuse. This paper reports experimental results from examination of the basic characteristics of micro-bubbles and disinfection of secondary effluent by air or ozone micro-bubbles. The results suggest that when micro-bubbles are applied in an ozonation system it is possible to reduce the reactor size, the amount of ozone decomposition equipment needed and the ozone dose rate.     

Characteristics of estrogen decomposition by ozonation.

Since the natural estrogens 17 beta-estradiol (E2) and estron (E1), and the synthetic estrogen 17 alpha-ethynyl estradiol (EE2) have strong endocrine disrupting effects and the tendency to persist in effluent from wastewater treatment plants, effective measures are needed to remove them from wastewater. In this research, to gain an understanding of the characteristics of estrogen decomposition by ozonation, experiments were conducted using effluent from an actual wastewater treatment plant. In this experiment, estrogen was added to effluent at a concentration of 200 ng/l and 20 ng/l before the ozonation experiments. The results showed 90% or more of estrogen concentration and estrogenic activity of E2, El and EE2 to be removed at an ozone dose of 1 mg/l. At an ozone dose of 3 mg/l, the estrogen concentration and estrogenic activity of E2, El and EE2 in the treated water fell below the detection limit. The removal rate was not influenced by the kind of estrogen. No generation of byproducts with estrogenic activity was observed. The authors conclude that estrogen in secondary treated wastewater can be almost entirely removed at the practical ozone dose rate applied for the purpose of disinfection, which is up to about 5 mg/l.     

Application of a virological tracer method for the assessment of pathogen removal by physicochemical treatment and chemical disinfection.

Coxsackie B3 (CoxB3) virus was used as a virological tracer for an assessment of the efficiency of pathogen removal by several typical physicochemical treatment and chemical disinfection processes, such as coagulation-filtration, ultra-filtration, and disinfection using chlorine and ozone, with regard to the pathogenic quality of the treated domestic wastewater for reuse purposes. The CoxB3 virus was seeded to sterilized secondary effluent to make a raw water of known pathogenic level. After applying the raw water to each treatment or disinfection process, the residual virus in the finished water was concentrated, and virus assay was carried out by the Tissue Culture Infectious Dose technique. TCID50 was used as an indicative parameter of CoxB3 virus in the raw and treated water. Parallel experiments were also conducted to evaluate the effectiveness of each process for the removal of coliform bacteria. It was noticed from the experiment that both coagulation-filtration and ultrafiltration could achieve substantial removal of TCID50 at about the same level (2-log removal). However, the effect of the two processes on the removal of coliform bacteria was much different: 2-log removal by coagulation-filtration and 4 to 5-log removal by ultrafiltration. The TCID50 removal correlates more closely with the removal of turbidity than that of coliform bacteria. Chlorine was found to be effective in coliform removal but almost had no effect on TCID50. As ozone was applied, a high removal of both coliform bacteria and TCID50 could be obtained.     

An antimicrobial polycationic sand filter for water disinfection

A new sand filtration water disinfection technology is developed which relies on the antimicrobial properties of hydrophobic polycations (N-hexylated polyethylenimine) covalently attached to the sand's surface. The efficacy of the filter disinfection process was evaluated both with water spiked with E. coli and with real aqueous effluent from a wastewater treatment plant. For the former, over 7-log reduction in bacterial count was achieved. With real environmental wastewater secondary effluent samples, the E. coli concentration reduction declined to under 2 logs. This reduced inactivation efficiency compared to the model aqueous sample is likely due to the particulate or colloidal matter present that diminishes the contact between the immobilized polycation and the suspended bacteria. Preliminary sand washing methods were tested to assess potential 'regeneration' approaches. Potential advantages of the proposed approach over conventional disinfection in terms of eliminating harmful by-products and reducing energy consumption are discussed.     

Safety of treated water for re-use purposes--comparison of filtration and disinfection processes.

A study was conducted on the distribution of pollutants in treated wastewater and the its safety for re-use purposes. Based on the results of a series of tertiary treatment experiments, the effects of three filtration processes, i.e. coagulation-filtration, ozonation-biological activated carbon filtration (O3-BAC) and ultrafiltration (UF), and two chemical disinfection processes, i.e. chlorination and ozonation, on the safety of water re-use were evaluated. It was found that the concentrations of the main pollutants in the secondary effluent and further filtered water follow a log-normal distribution and, therefore, a log-normal probabilistic function can be used to evaluate the suitability of the treated water for re-use purposes. Among the three filtration processes evaluated, UF is the most effective in turbidity removal but less effective in colour and COD removal, while coagulation-filtration and O3-BAC can ensure a good removal of all these pollutants. Regarding chemical disinfection, although chlorine is very effective in inactivation of coliform bacteria, it can not achieve a substantial decrease in viruses. As ozone is applied, effective virus removal can be achieved.     

SUVA as control parameter for the effective ozonation of organic pollutants in secondary effluent.

Recent research projects have shown a good suitability of the ozonation process to transform trace concentrations of most pharmaceuticals in wastewater treatment plant (WWTP) effluents. The concentrations of carbamazepine and 17 alpha-ethinylestradiol, for instance, were reduced below their detection limits by use of ozone dosages resulting in a specific ozone consumption of 0.5 mg O3/mg DOC0. At the same time a good disinfection performance was achieved. The given hygienic requirements of the EU bathing water directive (e.g. 2,000 N/100 mL faecal coliforms) are fulfilled without the formation of bromate (<10 microg/L). As technical control parameter of the ozonation process usually the residual ozone in the liquid phase or in the off-gas are used. However, at very low specific ozone consumptions, ozone reacts instantaneously with dissolved compounds and cannot be detected. Hence, alternative parameters should be used for effective operation control. The present paper evaluates the relation between UVA decrease and the removal of different compounds (endocrine disrupting compounds, pharmaceuticals, iodinated X-ray contrast media), microbial parameters and bromate formation. The results can be used as a guideline for the control of the oxidation performance at large scale ozonation units.     

UV disinfection of stabilization pond effluent: a feasible alternative for areas with land restriction

The purpose of this research was to determine the feasibility of a UV photoreactor for the disinfection of effluent from a polishing pond following a UASB reactor treating domestic wastewater. For this, a 20 mm diameter photoreactor (20.7 litre volume) equipped with four 30 W submerged low-pressure mercury arc lamps was used. Three tests with contact times and doses ranging from 45 to 90 s and from 16.9 to 31.3 mW s cm(-2) were carried out. Inactivation of total coliforms and Escherichia coli varied from 2.6 to 3.4 log-units, even with the presence of suspended solids in the range of 87 to 102 mg L(-1). These results have shown that UV radiation disinfection of pond effluents can be a feasible alternative in areas with land restriction.     

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.     

The basics of oxidants in water treatment. Part B: ozone reactions.

The oxidation of organic and inorganic compounds during ozonation can occur via ozone or OH radicals or a combination thereof. Ozone is an electrophile with a high selectivity. The reactions of ozone with inorganic compounds are typically fast and occur by an oxygen atom transfer reaction. Organic micropollutants are oxidised with ozone selectively. Ozone reacts mainly with double bonds, activated aromatic systems and non-protonated amines. The kinetics of direct ozone reactions depend strongly on the speciation (acid-base, metal complexation). The reaction of OH radicals with the majority of inorganic and organic compounds is nearly diffusion-controlled. The degree of oxidation by ozone and OH radicals is given by the corresponding kinetics and the ratio of the concentration of the two oxidants. Product formation from the ozonation of organic micropollutants has only been established for a few compounds. Numerous organic and inorganic ozonation disinfection/oxidation byproducts have been identified. The byproduct of main concern is bromate, which is formed in bromide-containing waters. A low drinking water standard of 10 microgL(-1) has been set for bromate. In certain cases (bromide > approximately 50 microgL(-1)), it may be necessary to use control measures to lower bromate formation (lowering of pH, ammonia addition, chlorination-ammonia process).     

Catalytic ozonation for odour removal of high temperature alumina refinery condensate

Odour emissions from aluminium processing can cause an impact on local communities surrounding such facilities. Of particular concern is fugitive odours emitted from the handling and use of refinery condensate streams, particularly the digestion condensate. This study evaluated the application of using catalytic ozonation to treat alumina refinery condensate in order to remove the potential emission of odourous compounds from the industrial wastewater. The technical challenges in treating the alumina refinery condensate are the high pH and temperatures of the wastewater effluent (over 80 °C and pH above 10) due the industrial process. The odour removal efficiencies for different catalysts (FeCl(3), MnO, and MnSO(4)) under experimental conditions in terms of controlled pH, temperature and ozone dosage were determined before and after ozone treatment using dynamic olfactometry. The result demonstrated that the addition of both FeCl(3) and MnO catalysts improved odour removal efficiencies during the ozonation of alumina condensates at similar pH and temperature conditions. FeCl(3) and MnO had similar enhancement for odour removal, however MnO was determined to be more appropriate than MnSO(4) for odour removal due to the colouration of the treated condensate.     

Evaluation of phytotoxic elements, trace elements and nutrients in a standardized crop plant, irrigated with raw wastewater treated by APT and ozone.

This project studied the benefits of applying Advanced Primary Treatment (APT) and ozone (O3) to raw wastewater destined for reuse in agriculture. The ozone was applied directly to raw wastewater, as well as to wastewater already treated with APT, and the results compared against a control sample of potable water. The experimental conditions that reported the best results was wastewater treated with O3 (at a dose of 4.8 mg/L, at pH 7, temperature 23 degrees C, for 1 hr), given that it met standards in force in Mexico with regard to micro-organism and heavy metal content. Under these conditions, after 15 min of ozonation, 100% destruction of the following bacteria was observed: V. cholerae, S. typhi as well as total and faecal coliforms. Destruction of helminth eggs and Giardia sp. took one hour. No phytotoxic elements or heavy metals were found. The balance of nutrients N:P:K (300:100:200 mg/kg) required for lettuce growth, was found in wastewater subjected to both treatment plans. However, ozone favoured the nitrification and assimilation of the nutrients, by contributing oxygen to the soil. Therefore, these conditions produced the greatest lettuce growth, the entire plant averaging 38 cm in length and 125 g. in weight. Moreover, a better appearance of the leaves was also noted.     

Helminth ova removal from wastewater for agriculture and aquaculture reuse.

In the new version of the World Health Organization (WHO), water reuse guidelines helminth ova are considered one of the main target pollutants to be removed from wastewater reuse for agriculture and aquaculture purposes. In spite of this, along with the fact that helminth ova have been considered the main health risk to wastewater reuse for agriculture for at least 20 years, relatively little research has been done to control helminth ova in the wastewater treatment field. This paper addresses (1) characteristics of helminth ova and differences with microorganisms; (2) the most frequent helminth ova genus found in wastewater; (3) helminth ova content in developed and developing countries wastewater; (4) reasons why conventional disinfection methods cannot be applied; (5) main removal mechanisms; and (6) processes that in practice have effectively removed or inactivated helminth ova.     

An overview of the integration of ozone systems in biological treatment steps.

Despite the well-known potential and performance of combined biological and ozonation processes for wastewater treatment, only few full-scale applications are published. Beside the synergistic effects of such process combination, which lead to oxidation of recalcitrant and inhibitory compounds or intermediates by enhancement of their biodegradability, the key for raising applicability is the improvement of the ozonation efficiency. An overview about the history and progress of full-scale applications, which deals with combined ozonation and biological treatment is given. Recently more than 40 applications exist, but many of them are not published. Therefore, a couple of selected not yet published applications have been mentioned in this paper. Landfill leachate and industrial wastewater treatment were mostly applicated, while treatment of municial wastewater treatment plant (WWTP) effluents are of increasing interest due to several advantages such as disinfection, decolourisation and removal of persistent dissolved organic carbon (DOC) for water re-use and groundwater recharge.     

Contribution of brominated organic disinfection by-products to the mutagenicity of drinking water.

The activity inducing chromosomal aberrations of the mixture of brominated disinfection by-products (DBPs) was approximately three times higher than that of the chlorinated counterparts for the same hypohalous acid dose. With the combination of chromosomal aberration test and a new analytical technique to differentiate total organic chlorine (TOCl) and total organic bromine (TOBr), it was found that TOBr was correlated to the mutagenicity of chlorinated waters. It was also implied that for a bromide-to-TOC ratio of 0.1 (mg/mg C), brominated DBPs could account for at least 29% of the total toxicity of DBPs formed during chlorination. On the other hand, bromate ion, a major ozonation DBP, was not a major contributor to the activity inducing chromosomal aberrations of the water treated with an ozone/chlorine sequential process. Therefore, ozonation is one possible option to reduce the health risk caused by DBPs even in the presence of bromide.     

Recalcitrant COD degradation by an integrated system of ozonation and membrane bioreactor.

In order to treat wastewater to a low residual COD-concentration such as 125 mg/L, classical biological treatment is not sufficient for many types of industry. This research focused on the integrated treatment of the wastewater of the paper industry, with a membrane bioreactor (MBR) and an oxidation step. The optimal configuration was examined. Screening tests with different types of oxidation showed that ozonation after biological treatment could reduce the COD with 40% with an ozone dose of 0.4-0.8g O3/g COD. BOD/COD ratio could be increased up to 0.19. Neither combination of ozone with UV and/or hydrogen peroxide nor the process H2O2/UV or (photo-)Fenton reagents gave any improvement in COD reduction or BOD increase, unless the doses were very high. Based on these results, an integrated system MBR-ozonation was designed, with recirculation of MBR effluent over ozonation. This test showed that reduction of COD up to 125 mg/L immediately behind the MBR required a lot of ozone. A technically feasible solution was to discharge the water after an extra ozonation step, which resulted in a high total ozone dosage. The alternative, the consecutive treatment activated sludge-ozonation-activated sludge, did not give a better COD-removal with the same ozone dose as the integrated concept. The economic evaluation proves that the integrated chemical and biological treatment is expensive for the paper industry if a low discharge limit of COD has to be complied with.     

Adsorption of viruses to soil: impact of anaerobic treatment.

The adsorption of viruses in untreated flushed dairy manure wastewater (FDMW), anaerobically digested flushed dairy manure wastewater (ADFDMW) and groundwater to sandy soil was investigated. Batch adsorption studies showed differential adsorption of viruses in groundwater to soil. Less than 75% of PRD1 and MS2 added to groundwater adsorbed after 1 h, but greater than 95% of phiX174 and poliovirus 1 adsorbed to the soil. Adsorption differences in groundwater were related to the isoelectric points of the viruses. Suspending phages in untreated and treated wastewater reduced adsorption compared with groundwater. For MS2, more phages were adsorbed using ADFDMW than with FDMW. Adsorption of poliovirus 1 was not affected by FDMW and ADFDMW. Small column studies (6 x 2.5 cm) produced a similar trend in that adsorption was observed with groundwater and both FDMW and ADFDMW reduced virus adsorption. Groundwater, FDMW or ADFDMW did not affect the adsorption of poliovirus 1 in column studies. The major difference between FDMW and ADFDMW was in mobilisation of adsorbed viruses. The application of FDMW to soil columns with adsorbed viruses caused significantly more viruses to be mobilised than did the application of rainwater or ADFDMW. These results showed that treating FDMW by anaerobic digestion increased the adsorption of viruses to soil and decreased detachment of adsorbed viruses. As the potential for new zoonotic pathogens becomes known, the treatment of animal wastes may become mandatory. The assessment and management of viruses in manure for addressing possible risk to animal and human health is of interest.     

Long-term effects of the ozonation of the sludge recycling stream on excess sludge reduction and biomass activity at full-scale

This paper presents a full-scale experience of sludge minimization by means of short contact time ozonation in a wastewater treatment plant (WWTP) mainly fed on textile wastewater. The WWTP performance over a 3-year operational data series was analysed and compared with a two-year operation with sludge ozonation. Lab-scale respirometric tests were also performed to characterize biomass activity upstream and downstream of the ozone contact reactor. Results suggest that sludge ozonation: (1) is capable of decreasing excess sludge production by 17%; (2) partially decreases both N removal, by lowering the denitrification capacity, and P removal, by reducing biomass synthesis; (3) increases the decay rate from the typical value of 0.62 d(-1) to 1.3 d(-1); (4) decreases the heterotrophic growth yield from the typical value of 0.67 to 0.58 gCOD/gCOD.     

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.     

Removal of endocrine-disrupting chemicals by ozonation in sewage treatment.

Treatment experiments by two laboratory scale semi-batch reactors and a demonstration scale process were both carried out to evaluate endocrine disrupting chemical removal characteristics by ozonation in sewage treatment. In the semi-batch mode experiments, secondary effluent and primary effluen of sewage treatment plants were ozonated respectively. Behaviour of brominated by-products was also evaluated. The results based on these studies indicated that estrogenicity in wastewater can be removed by ozonation effectively. The condition of ozonation until dissolved ozone concentration increased to 0.1 mg/L, which corresponded to 1 mgO3/mgC and 0.4 mgO3/mgC of ozone consumption per initial DOC for secondary effluent and primary effluent, respectively, is proposed as an appropriate operational condition for efficient removal of EDCs as well as UV254 and SUVA without production of brominated by-products.     

Antimicrobial resistance of fecal indicators in disinfected wastewater

The main objective of the study was to assess the potential of three systems (UV irradiation, ozonation, and micro/ultrafiltration) operated in a pilot scale in removal of antimicrobial-resistant fecal bacteria from secondary effluent of the local wastewater treatment plant (700,000 population equivalent). The effectiveness of the processes was analysed using the removal ratio of fecal indicators (Escherichia coli and Enterococcus spp.). The susceptibility of fecal indicators to antimicrobial agents important in human therapy was examined. Resistance to nitrofurantoin and erythromycin was common among enterococci and followed by resistance to fluoroquinolones and tetracycline. Resistance to high-level aminoglycosides and glycopeptides was also observed. E. coli isolates were most frequently resistant to penicillins and tetracycline. The extended-spectrum beta-lactamase-producing E. coli was detected once, after ozonation. Substantial attention should be paid to the E. coli and enterococci resistant to three or more chemical classes of antimicrobials (MAR), which in general constituted up to 15 and 49% of the tested isolates, respectively. Although the applied methods were effective in elimination of fecal indicators (removal efficiency up to 99.99%), special attention has to be paid to the application of sufficient disinfection and operation conditions to avoid selection of antimicrobial resistant bacteria.