Chemical and Microbiological Quality of Effluents from Different On-Site Wastewater Treatment Systems across Finland and Sweden

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.

Efficiency of Private Household Sand Filters in Removing Nutrients and Microbes from Wastewater in Finland

“…Sand filters with or without a phosphorus-adsorbing layer have proven to be the most cost-effective and environmentally-friendly approaches if long-term use and renovation needs are considered [7,8]. It has been revealed [8][9][10], however, that the treatment efficiency of sand filters can be highly variable.…”

“…Sand filters with or without a phosphorus-adsorbing layer have proven to be the most cost-effective and environmentally-friendly approaches if long-term use and renovation needs are considered [7,8]. It has been revealed [8][9][10], however, that the treatment efficiency of sand filters can be highly variable. Studies of many different sand filters demonstrated that those filters with P-adsorbing media were better at reducing phosphorus and nitrogen than filters without any adsorbing media [8,10].…”

“…It has been revealed [8][9][10], however, that the treatment efficiency of sand filters can be highly variable. Studies of many different sand filters demonstrated that those filters with P-adsorbing media were better at reducing phosphorus and nitrogen than filters without any adsorbing media [8,10]. However, it has been reported that sand filters without adsorbing media were able to reduce the levels of phosphorus and nitrogen better than systems with P-adsorbing gypsum or different ferro sulfate media [9].…”

“…However, it has been reported that sand filters without adsorbing media were able to reduce the levels of phosphorus and nitrogen better than systems with P-adsorbing gypsum or different ferro sulfate media [9]. Furthermore, sand filters without P-adsorbent media were able to remove BOD better than filters with a P-adsorbent media [8], although others have reported contrasting results [9]. However, the removal of BOD was at the required level in most of the sand filters, irrespective of whether they had P-adsorbing media [8,9], as confirmed in a later study [10].…”

How Efficient Are Semi-Natural Ponds in Assimilating Wastewater Effluents? Application to Fuente de Piedra Ramsar, Mediterranean Salt Lake (South of Spain)

“…Our wetland system shows similar efficiency in bacteria and nutrient reduction to other wastewater treatment systems [44,45]. However, natural wetland-systems are usually cheaper to build and maintain [46,47].…”