ABSTRACT
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.
Subject(s)
Waste Disposal, Fluid/methods , Water Microbiology , Water Purification/methods , Water Supply , Agriculture , Bacteria/isolation & purification , Conservation of Natural Resources , Filtration , Phosphorus/isolation & purification , Silicon Dioxide , Ultraviolet RaysABSTRACT
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.
