## Skuteczność oczyszczania ścieków w przydomowej oczyszczalni z wykorzystaniem zmodyfikowanego filtru żwirowo-piaskowego

### Krzysztof Chmielowski

#### Abstract

Untreated domestic sewerage still poses a serious threat to the environment in rural areas. The lack of simultaneous construction of water supply and sewerage systems in rural areas contributed to the significant imbalance between water supply and sewage discharge. Raw sewage, entering the natural receiver, cause rapid degradation of life and contribute to the biological imbalance in the environment. Untreated sewage can cause the deterioration of water quality in private wells and may even lead to its total contamination. In areas, where it is impossible to implement collective sewerage systems, there is an alternative in the form of buildings septic tanks or household sewage treatment plants. The development o fhousehold sewage treatment plants in Poland has been observed for decades. There were 4000 household sewage treatment plants in Poland has been observed for decades. There were 4000 household sewage treatment plants registered in 1998, while in 1999 this number increased to 18054. A rapid increase was observed in subsequent years, i.e. in 2008 there were 51,943 registered household sewage treatment plants, in 2010 this number increased to about 81 thousand and in 2011 about 103 thousand treatment plants were registered. In the near future a dramatic increase in the number of newly built household sewage treatment plants is expected. The aim of this study was to analyze the efficiency of domestic sewage treatment in a household seawage treatment plant with a modified vertical flow sand and gravel filter. The aim was achieved by performing preliminary laboratory studies using a fragmentary “M1” model in a scale 1:1, and then by construction of a modified prototype of ‘F1’ filter in the field and determining its effectiveness under field conditions. on this basis, the author proposed an innovative solution – a modified vertical flow gravel and sand filter. Currently, the procedures related to the patent application of the prototype of the modified gravel and sand filter are being underway. the original solution in the vertical flow sand filter consisted in: - placement of a protective layer of small pebbles before the filtration (sand) layer, - -application of innovative sewage distribution system in the form of the proprietary solution, - reduction of the filter surface as compared to conventional solutions. The classic vertical flow sand filters occupy a significant surface (25-30 m2 for a five persons househols). This study attempts to reduce the dimensions of the filter on the plan. An important element of the beds modification is the design of a suitable sewage distribution system in order to utilize the filter layer as much as possible. The spacing of sewage distribution drains on the surface of the filter bed in conventional solutions is very large and range up to 200 cm. With thickness of the proper filtration layer from 60 to 100 cm the filter bed may be unevenly loaded. By increasing the use of the filter layer and introducing an additional protective layer (made of small pebbles) one can significantly reduce the dimensions of vertical flow sand filter while at the same time maintaining the acceptable level of the filtrate quality. The study included the determination of physical and chemical indicators of pollution in sewage flowing into and out of the filter: BOD5, CODCr, dissolved oxygen, total suspended solids, ph, total phosdphorus, anomnuium nitrogen NH4, organic nitrogen, total Kjeldahl nitrogen, nitrite nitrogen NO2, nitrate nitrogen NO3, and total nitrogen (the values of physical and chemical indicators of sewage collected from the following depths of the filter bed were determined: 10 cm, 30 cm, 50 cm, 90 cm). Moreover, the abundance of microbial indicators of sewage pollution 9coliform bacteria, Escherichia coli, Enterococus faecalis, Salmonella spp, Shigella spp, and Clostridium perfingens) was determined in sewage flowing into the filter, at the outflow from the gravel layer and at the outflow the sand layer. Based out the results of the analyzes it is recommended to use a protective layer made of small pebbles with a normal grain size of d10= 1.66 mm and thickness of 50 cm. Under this layer there should be a proper filtration layer made of rinsed sand with normal diameter of d10= 0,40 mm and thickness of at least 60 cm. An important advantage of the modified vertical flow gravel and sand filter it its small surface (1.15 m2•M-1)while in the classical solution it is even up to 7 m2•M-1. Taking into consideration that the removal of pollutants is most intense at the initial depth of the protective layer, it is very important to evenly distribute the pre-treated sewage over the surface of the protective layer made of small pebbles. The use of innovative sewage distribution system allowed the optimal use of the filter beds surface during the study period. Due to the large amounts of biogenic compounds in treated sewage, the use of the modified vertical flow gravel and sand filter is not recommended when discharging treated sewage into stagnant water bodies and lakes.