Performic acid for advanced wastewater disinfection.

The disinfection efficiency of performic acid (PFA) against various microbial contaminants has been studied in municipal secondary effluent. The study demonstrated that PFA provides rapid, efficient and safe disinfection, degrading both bacteria and viruses even at low doses. The resistance order starting from the most resistant microorganism is as follows: MS2-coliphages > DNA-coliphages > enterococci and Escherichia coli. PFA is also efficient in the elimination of Salmonella spp., Clostridium perfringens spores and Giardia cysts. The results showed that a PFA dose as low as 0.5-1 mg L(-1) with contact time of 10 min was efficient in achieving and maintaining for 72 h the disinfection level required for unrestricted agricultural water reuse (≤3 log units for faecal coliforms). However, the optimal dose will depend on the quality of wastewater. Regarding the formation of by-products during disinfection with PFA, very low amounts of hydrogen peroxide and organic per-acids were observed; active oxygen was not detected. The amounts of adsorbable organically bound halogens (AOX) compounds formed were significantly lower compared to the amounts generated during chlorine disinfection. This chlorine-free solution enables compliance with microbiological criteria for various water reuse applications and is already on the market for advanced disinfection.

Airborne enteric micro-organisms and ammonia levels in diaper-changing rooms in kindergartens.

AIMS: We evaluated risks associated with diaper changing in Finnish kindergartens where children were using either modern disposable paper or reusable cloth diapers. METHODS AND RESULTS: We determined enteric micro-organisms and ammonia in diaper-changing rooms in four kindergartens in autumn and winter in the ambient air. No coliphages were detected in the air. The numbers of faecal coliforms and enterococci in air were typically low regardless of whether the children used either paper or cloth diapers. Ammonia concentrations increased over the background level because of diaper changing. CONCLUSIONS: The numbers of bacteria or coliphages are not expected to pose any high air hygiene risks, and increased ammonia air concentrations are unlikely to impair the health of staff or children when diapers are changed in modern kindergartens. However, increased ammonia gas concentrations indicate that some other diaper-related gas-phase emissions should be studied to understand better diaper-related health risks. SIGNIFICANCE AND IMPACT OF THE STUDY: Modern reusable cloth baby diapers and the modern paper baby diapers used in this study are equally safe with respect to risks from airborne virus, bacteria or ammonia.

Measurement and control practices in Finnish wastewater networks.

In this paper, we describe measurement and control practices in Finnish wastewater networks. We have surveyed the 14 largest wastewater treatment plants in the country, which account for approximately 40% of total Finnish treatment capacity. It was found that these plants still only rely on a few, traditional measurement techniques. The treatment processes could be improved, and the treatment could be made more energy-efficient by installing modern instrumentation. We review some recent developments in wastewater plant instrumentation technology and suggest improvements to Finnish plants.

Use of sewer on-line total solids data in wastewater treatment plant modelling.

We describe a neural network model of a municipal wastewater treatment plant (WWTP) in which on-line total solids (TS) sewer data generated by a novel microwave sensor is used as a model input variable. The predictive performance of the model is compared with and without sewer data and with modelling with a traditional linear multiple linear regression (MLR) model. In addition, the benefits of using neural networks are discussed. According to our results, the neural network based MLP (multilayer perceptron) model provides a better estimate than the corresponding MLR model of WWTP effluent TS load. The inclusion of sewer TS data as an input variable improved the performance of the models. The results suggest that increased on-line sensing of WWTPs should be stressed and that neural networks are useful as a modelling tool due to their capability of handling the nonlinear and dynamic data of sewer and WWTP systems.

Nitrogen reduction in wastewater treatment using different anox-circulation flow rates and ethanol as a carbon source.

We studied the optimization of nitrogen reduction from municipal wastewater in a laboratory-scale modified Ludzack-Ettinger activated sludge wastewater treatment plant (WWTP). The unit consisted of primary denitrification, secondary nitrification, a sludge clarifier and a post-denitrification unit. The process simulates the Kuopio WWTP, which provided the influent utilized. We describe the effect of varying anox-circulation schemes on the nitrogen removal efficiency. We further compare the denitrification efficiencies of ethanol and methanol applied in the post-denitrification unit, and compare the properties and costs of these chemicals as carbon sources. Maximum efficiency of total nitrogen removal (70.8%) was obtained with 256% anox-circulation. The process was, however, not very sensitive, as a wide range of 150-400% of anox-circulations gave good results for nitrogen reduction. The unit achieved high BOD, and COD reductions of wastewater also when nitrogen reduction was moderate. The addition of 40 mg/L/day of ethanol to the post-denitrification tank meant that the nitrate-levels of effluent could be controlled to below 10 mg/L of nitrate nitrogen. Methanol and ethanol were equally effective for denitrification. The use of ethanol instead of methanol could reduce treatment costs by 30% to 0.02 E/m3 of treated wastewater according to 2008 market prices.

Survival of enteric bacteria and coliphage MS2 in pure human urine.

AIMS: The survival of Escherichia coli, Salmonella enterica serovar Typhimurium, Enterococcus faecalis and coliphage MS2 was studied in stored, fresh and diluted (1 : 1) human urine at 15 and 30 degrees C. METHODS AND RESULTS: Survival rate was studied by the plate count method. All the organisms showed rapid inactivation in stored urine, but they survived better in diluted and fresh urine. The high pH level and temperature were the major factors found to influence the survival of the micro-organisms with the survival rate being higher at 15 degrees C than at 30 degrees C. CONCLUSIONS: The destruction of all micro-organisms in stored urine required <1 week at 30 degrees C. Thus, the storage of urine is a useful way to reduce the risk of contamination while using urine as a fertilizer. SIGNIFICANCE AND IMPACT OF THE STUDY: The urine fertilization is aimed for the developing countries and the high temperatures in these countries may hasten the destruction of micro-organisms in urine. On the contrary, a higher survival rate of these organisms in fresh and diluted urine is a public health concern because the dilution of urine with water is likely to happen during flushing.

On-line microwave total solids sensoring in sewage characterization.

We describe a novel application for a microwave on-line sensor to measure the total solids (TS) load entering a municipal wastewater treatment plant (WWTP) from slaughterhouse sewage and some sanitary wastewaters. Measuring this kind of wastewater stream is very challenging, because it contains a high, but varying organic load with nitrogen, phosphorus and microorganisms. The reliability of the measured signal was studied by comparison with laboratory analyses and a correlation is presented of TS-value with other parameters that are typically followed in a wastewater treatment process. The results suggest that on-line microwave sensoring could be used to monitor total solids in wastewater influent. Our results show that the on-line microwave sensor and laboratory reference analyses give similar results with a good correlation between the two techniques. Furthermore, we demonstrate that the total solids values correlate well with conductivity, total nitrogen and BOD(7) values but not with phosphorus, pH and temperature.

Dissolved air flotation (DAF) for primary and tertiary treatment of municipal wastewaters.

Tertiary treatment of municipal wastewater by dissolved air flotation was studied on a pilot-scale. The effects of coagulant dose, flocculation pattern, dispersion water recycle ratio and hydraulic surface load on process performance were evaluated. The treatment of primary effluents by dissolved air flotation was investigated to assess the suitability of this process for the treatment of heavily polluted effluents and wastewater treatment plant by-passes. The tertiary dissolved air flotation process typically achieved 90-99% reductions in the numbers of enteric microbes (total coliforms, enterococci and F-RNA coliphages). The average reductions of total phosphorus and chemical oxygen demand were 55-81% and 28-39%, respectively. Increasing the polyaluminium chloride coagulant dose from 2 to 10 mgAl(3+) l(-1) and the dispersion water recycle ratio from 11 to 22% improved the efficiency of the process. Changes in the flocculation conditions (range of G-values 10-55 s(-1); retention time 4-8 min) and hydraulic surface load (5 or 10 m h(-1)) did not clearly affect the process efficiency. The dissolved air flotation process decreased the numbers of enteric microbes and reduced total phosphorus, chemical oxygen demand and suspended solids from the primary treated wastewaters on average by 98-99.8%, 90%, 47% and 77%, respectively. The dissolved air flotation process was demonstrated to be a suitable method for efficient tertiary treatment of wastewaters, as well as for the elimination of peak pollution loads or by-pass wastewaters during the treatment plant overloading situations.

Contamination of surface run-off water and soil in two horse paddocks.

Increased stabling of horses near to cities has led to interest in the environmental effects of paddocks. In this study, the contamination of horse paddocks was examined by determining the nutrient and micro-organism contents in the surface run-off waters and the electrical conductivity, pH and phosphorus, potassium and nitrate contents of top soils. Two open-stable paddocks were studied, one cleaned and the other left uncleaned, with a stocking density of 37.5 animalsha(-1) in both. The feeding and drinking places were the most contaminated areas of both paddocks. In spring, after seven months of use, the nutrient concentrations in the surface run-off water from paddocks were 3.4-18.8mg/l for total phosphorus, 3.0-15.0mg/l for phosphate and 18.3-140.0mg/l for total nitrogen, indicating a risk to surface waters. Summer rain generated surface run-off, especially from the feeding area of the stock-free uncleaned paddock.

Inactivation of enteric microorganisms with chemical disinfectants, UV irradiation and combined chemical/UV treatments.

The relative disinfection efficiencies of peracetic acid (PAA), hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl) against Escherichia coli, Enterococcus faecalis, Salmonella enteritidis and coliphage MS2 virus were studied in laboratory-scale experiments. This study also evaluated the efficiency of combined PAA/ultraviolet irradiation (UV) and H2O2/UV treatments to determine if the microbial inactivation was synergistic. Microbial cultures were added into a synthetic wastewater-like test medium and treated by chemical disinfectants with a 10 min contact time, UV irradiation or the combination of chemical and UV treatments. A peracetic acid dose of 3 mg/l resulted in approximately 2-3 log enteric bacterial reductions, whereas 7-15 mg/l PAA was needed to achieve 1-1.5 log coliphage MS2 reductions. Doses of 3-150 mg/l hydrogen peroxide achieved below 0.2 log microbial reductions. Sodium hypochlorite treatments caused 0.3-1 log microbial reductions at an 18 mg/l chlorine dose, while 2.6 log reductions of E. faecalis were achieved at a 12 mg/l chlorine dose. The results indicate that PAA could represent a good alternative to chlorine compounds in disinfection procedures, especially in wastewaters containing easily oxidizable organic matter. Hydrogen peroxide is not an efficient disinfectant against enteric microorganisms in wastewaters. The combined PAA/UV disinfection showed increased disinfection efficiency and synergistic benefits with all the enteric bacteria tested but lower synergies for the coliphage MS2. This suggests that this method could improve the efficiency and reliability of disinfection in wastewater treatment plants. The combined H2O2/UV disinfection only slightly influenced the microbial reductions compared to UV treatments and showed some antagonism and no synergies.

Peracetic acid (PAA) disinfection of primary, secondary and tertiary treated municipal wastewaters.

The efficiency of peracetic acid (PAA) disinfection against enteric bacteria and viruses in municipal wastewaters was studied in pilot-scale. Disinfection pilot-plant was fed with the primary or secondary effluent of Kuopio municipal wastewater treatment plant or tertiary effluent from the pilot-scale dissolved air flotation (DAF) unit. Disinfectant doses ranged from 2 to 7 mg/l PAA in the secondary and tertiary effluents, and from 5 to 15 mg/l PAA in the primary effluents. Disinfection contact times were 4-27 min. Disinfection of secondary and tertiary effluents with 2-7 mg/l PAA and 27 min contact time achieved around 3 log reductions of total coliforms (TC) and enterococci (EC). PAA disinfection also significantly improved the hygienic quality of the primary effluents: 10-15 mg/l PAA achieved 3-4 log reductions of TC and EC, 5 mg/l PAA resulting in below 2 log reductions. F-RNA coliphages were more resistant against the PAA disinfection and around 1 log reductions of these enteric viruses were typically achieved in the disinfection treatments of the primary, secondary and tertiary effluents. Most of the microbial reductions occurred during the first 4-18 min of contact time, depending on the PAA dose and microorganism. The PAA disinfection efficiency remained relatively constant in the secondary and tertiary effluents, despite of small changes of wastewater quality (COD, SS, turbidity, 253.7 nm transmittance) or temperature. The disinfection efficiency clearly decreased in the primary effluents with substantially higher microbial, organic matter and suspended solids concentrations. The results demonstrated that PAA could be a good alternative disinfection method for elimination of enteric microbes from different wastewaters.

Mycorrhizal growth in pure cultures in the presence of pesticides.

The effects of pesticides on 64 ectomycorrhizal fungi of boreal forest trees were studied in vitro. The pesticides (fungicides: benomyl, chlorothalonil, copper oxychloride, maneb and propiconazole; herbicides: chlorthiamid, glyphosate, hexazinone, linuron and terbuthylazine; insecticide: cypermethrin) were selected as those commonly used in Nordic forest nurseries and afforestation sites. In general, the fungicides proved to be more toxic to ectomycorrhizal fungi than the herbicides and cypermethrin. The fungicides, chlorothalonil and propiconazole, had the clearest inhibitory effect on growth of mycorrhizal fungi. Conversely, maneb, glyphosate and terbuthylazine stimulated the growth of some mycorrhizal fungi. Leccinum versipelle and L. scabrum, Paxillus involutus and Cenococcum geophilum were the most sensitive ectomycorrhizal fungi to the various pesticides.

The role of ferrioxamine E in pre-enrichment medium for determining Salmonella in environmental samples according to ISO method.

The effect of a siderophoric compound, ferrioxamine E, in the pre-enrichment broth on determining of Salmonella infantis in environmental samples was tested with combination of various pre-enrichment times and enrichment temperatures of 37 and 43 degrees C. Ferrioxamine E slightly improved the determination efficiency of this bacterium but the pre-enrichment time could not be reduced below 17 hours. The enrichment temperature of 43 degrees C was better than of 37 degrees C. The mixing ratios of 1:100 or 1:1000 for samples and pre-enrichment broth were more successful than the ratio of 1:10 as recommended by ISO.

Runoff of faecal microorganisms and nutrients from perennial grass ley after application of slurry and mineral fertiliser.

Perennial grass was fertilised with cattle slurry either surface-spread or injected into the soil. Slurry was spread once (early summer) in 1996 and 1997 and twice (both summer and autumn) in 1998 and 1999. The control was mineral fertilisation in summer. Faecal microbial numbers in surface runoff water were very high in late June 1998 soon after very heavy rains even though the last slurry application had been made almost one year earlier. There was no clear difference between slurry spreading methods. Autumn spreading of slurry lead to high microbial levels in runoff waters and water hygiene was protected better by slurry injection than by surface spreading. In spring, after snow melt, some faecal microorganisms were found in surface runoff water and the numbers of faecal microorganisms were less from plots with slurry surface spreading than those with slurry-injection. Losses of total phosphorus (TP) and total nitrogen (TN) in surface runoff were 2.7 and 7.7 kg/ha respectively from grass with surface-spread slurry in winter 1998-1999. The injection of slurry decreased TP and TN runoff by an average of 81% and 73% respectively. In 1999 there was little runoff because the summer was sunny and dry.

Removal of microbes from municipal wastewater effluent by rapid sand filtration and subsequent UV irradiation.

The elimination of wastewater microbes is often necessary when effluent receiving waters are reused for different purposes e.g. for irrigation or as a raw water source of drinking water. In the present study, rapid sand filtration (SF) combined with the use of polyaluminium chloride coagulation was used as a pre-treatment to improve the quality of wastewater effluent before further treatment with UV irradiation. Pilot-scale experiments were run in four treatment plants in Finland. Treatment performance was followed by measuring physical and microbial parameters. Rapid sand filtration reduced suspended solids, turbidity and colour of effluents by about 90%, 70-80% and 20-50% respectively. It also improved the UV transmittance of water by up to 20%. Microbes and phosphorus were reduced by 90-99% and to 0.05 mg/L respectively. UV irradiation further reduced the number of microbes up to 99.9%. The efficiency of UV doses in pilot UV reactors was confirmed with collimated-beam device determinations and with added FRNA phages. More than 99.9% reduction of MS2 was achieved with the dose of 140mWs/cm2 in pilot UV reactors. Rapid sand filtration and the subsequent UV irradiation reduced the number of all the tested microbes to a low level, often below the detection limit. Suspended solids and the water turbidity were reduced to 1-2 mg/L and approximately 1 NTU respectively.

Determination of salmonellae from municipal wastewaters.

This study compared the efficiency of culture methods for salmonellae detection in wastewaters collected from three Finnish municipal treatment plants and from one laboratory-scale plant. The performance of one-step enrichment in Preuss tetrathionate broth was better than that of two-step enrichment (buffered peptone water pre-enrichment (BPW) and selective enrichment in Rappaport-Vassiliadis (RV) medium. The best combinations for Salmonella isolation were xylose-lysine-deoxycholate (XLD) and Rambach (RB) agars after Preuss enrichment and did not differ when brilliant green-magnesium chloride (BM) or brilliant green phenol red (BP) agars were used. The two-step enrichment inhibited the growth of both salmonellae and interfering accompanying flora. Salmonella-positive plates were generally easier to read when inoculated from RV than from Preuss medium because of less growth of competing flora. XLD and BM agars supported growth of salmonellae and inhibited growth of competing flora better than BP and Rambach agars. XLD and BM agars gave the highest numbers of salmonellae isolations but XLD and Rambach agars gave the best differentiation. Salmonella levels were < 3- > 1100 MPN/100 mL.

Work-related symptoms and Salmonella antibodies among wastewater treatment plant workers.

Wastewater treatment plant workers are exposed to microbes, including Salmonella, but the prevalence of antibodies against Salmonella species or serovars in their serum samples has not been studied. Antibodies against Salmonella Infantis and lipopolysaccharide antigen common to S. Enteritidis and S. Typhimurium in immunoglobulin classes IgA, IgM and IgG were measured from 79 serum samples of wastewater treatment plant workers and from 79 blood donor samples. Faecal samples for Salmonella and Campylobacter were studied. Gastrointestinal, dermal and other symptoms were compared between 81 wastewater treatment plant workers and 89 food-processing workers. The blood donors had more antibodies against all of the tested antigens expect for S. Infantis in IgM and IgA classes, even though the wastewater treatment plant workers had more gastrointestinal symptoms than the controls. No Salmonella or Campylobacter were found in any faecal samples. Salmonella is not a probable cause of symptoms among wastewater treatment plant workers.

Salmonella in animal slurry can be destroyed by aeration at low temperatures.

Cattle and other animals infected by Salmonella can emit high numbers of these bacteria. To determine an effective means for reducing this bacterial group in animal slurry, samples were subjected to aeration in laboratory experiments and in farm-scale slurry tanks. A clear reduction in Salmonella levels was found in laboratory experiments at temperatures from 4 to 40 degrees C. Aeration in farm-scale slurry tanks increased the temperature above the ambient temperatures (often less than 0 degrees C) to maxima ranging between 19 and 40 degrees C. Farm-scale aeration results in similar reductions in Salmonella as those achieved in laboratory experiments. Thus, reductions, ranging from greater than 99% of the initial number to no detectable Salmonella, could be reached after 2-5 weeks using aeration processes with cattle slurries contaminated by Salm. infantis or pig slurry contaminated by Salm. typhimurium. These results suggest that farmers can control the spread of Salmonella from slurry to agricultural fields. The reduction mechanisms remain unknown, though the increase in pH (to 7 x 6-9 x 0) found in slurries after aeration might exert a decreasing effect on these bacteria.