Abstract
Domestic wastewaters, which cannot be disposed through sewage networks, must be treated with different on-site treatment systems; these are usually commercial, small-scale treatment plants or built sand filters. These systems are usually maintained by the house’s inhabitants. This study was achieved by analysing the chemical and microbiological data of 717 effluents collected in Finland and Sweden. There were inadequate reductions in 31% of phosphorus effluents, 22% of nitrogen effluents and 5% of biological oxygen demand compounds. The addition of a coagulant capable of precipitating phosphorus improved the performance of sand filters and biorotors. There are no legally binding limitations on the number of enteric microorganisms that can be present in an effluent, but the number of Escherichia coli and enterococci exceeded more than 100 colony forming units per 100 mL in 59% and 53% effluents studied, with the highest numbers for these indicators being more than 100,000 cfu per 100 mL. The number of E. coli and enterococci were lower when the concentration of phosphorus in effluent was less than 1 mg/L. The treatment efficiency varied extensively, even between similar plant models, possibly due to either irregular use, or after long pauses, when they were not being used. In addition, it is possible that the end users are not capable of properly maintaining these wastewater treatment plants.
Highlights
In 2013, 18% of the total population of 5.5 million in Finland, and 13% of the 9.7 million inhabitants in Sweden, were living in rural areas without connections to sewage networks and wastewater treatment plants [1]
Phosphorus reduction is the most critical parameter when evaluating the performance of different small-scale wastewater treatment units, since it was most often the P-reduction which exceeded the set value calculated from the Finnish limits [3]
The P-reduction was successful with most sand filters and biorotors using coagulants, i.e., the vast majority; 88% of biorotors and 82% of sand filters produced effluent with P-concentrations of ≤5.5 mg/L
Summary
In 2013, 18% of the total population of 5.5 million in Finland, and 13% of the 9.7 million inhabitants in Sweden, were living in rural areas without connections to sewage networks and wastewater treatment plants [1]. There are recent treatment analytical plants works are which document long-term performances or a few batch reactors, operating continuously or discontinuously, or biofilters and biorotors Most of these small-scale treatment units or sand filters [6,7,8,9,10,11,12]. All of the treatment number of sand filter effluents sampled was 191 and and those they originated from 27 different unitsThe selected treated both black and grey wastewaters, units which aimed to treat sand only filters, all of which were situated in Finland. Entrepreneurs using local sand and gravel, but commercial pipes and pumps,plants and they typically They were divided into filtersmade withand andinstalled without by specific sites, originated from 135 different treatment plants, many P-binding companies.material. They were divided into filters with and without specific P‐binding material sites, and
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