In order to avoid the problem of stoppage in the filters of vertical filtration, we tried to search for the filter media which was coarse and could clean the wastewater to the allowable contamination level. For this purpose the dolomite chippings were chosen and the modelling investigation was performed. Two modelled filters taking 0.2 square m area each were equipped: one was filled with the sand and the other was filled with the dolomite chippings. The results revealed that the initial contamination of the wastewater had a much bigger influence on the wastewater cleaning process than the hydraulic load. The wastewater was cleaned with the efficiency of 95.9% and never exceeded the allowable level of 30 mg O2 LE-1 in the dolomite chippings filter during the trial with the hydraulic load 0.03 m**3 mE-2 dE-1. When the hydraulic load was doubled the efficiency of the wastewater cleaning process decreased to 80.5% and the dependence of the cleaning process on the initial contamination of the wastewater increased. In order to ensure the successful removal of the easily decomposing organic pollutants from the wastewater up to their allowable contamination level, the quantity of the pollutants in the untreated wastewater must not exceed 220 mg O2 LE-1.

The possibilities to use other media instead of the sand in the filters of vertical flow are analysed in the article. The media used has to be inexpensive and its possibilities to clean the wastewater have to surpass that of the sand. The modelling of the wastewater treatment in the vertical flow filters was carried out in 2008 at the Water Research Institute of the Faculty of Water and Land Management of Lithuanian University of Agriculture. Dolomite powder was chosen for the investigation. Two models of 0.2 square m filters were made: one was filled with the sand, but the other was filled with the dolomite powder. It was found that the dolomite filter was less reactive to the primary contamination of the wastewater with the organic pollutants: when their amount rose from 320 to 460 mg O2 LE-1 according to the BOD7 index, the amount of the pollutants in the wastewater cleaned with the dolomite powder filter rose from 1.4 to 3.1 and amount in the wastewater which passed the sand filter rose from 0.5 to 13.9 mg O2 LE-1. General phosphorus was removed with the efficiency of 99.9% in the dolomite powder filter (and only with the efficiency of 87.0% in the sand filter). Therefore the dolomite powder filter will be removing phosphorus from the wastewater to the allowable contamination level for a much longer period. General nitrogen was cleaned with the effectiveness of 13.0% in the dolomite powder filter. Therefore, it is necessary to use additional means for its removal from the wastewater in the vertical filters with the output higher than 5 m**3 dE-1.

The article explores the possibility of the vertical filter instead of sand used for more coarse media for recharging, which would reduce the risk of freezing and clogging and ensure the cleaning of wastewater up to the limits. For this purpose the dolomite chippings have been chosen for research. It was equipped with two 0.2 m2 filters area: one of their models was 0.4 m dolomite chippings layer, the other 0.8 m. They have been loaded by the wastewater after the primary cleaning in the septic system. Medium contamination in organic pollutants have been 358 mg O2 LE-1, Ptotal 14.6 mg LE-1, Ntotal 108.5 mg LE-1, suspended solids 161.1 mg LE-1, pH 7.8. Hydraulic load of the filters was 0.03 m3 mE-2 dE-1. Wastewater flowing through a vertical sand layer by an average of 98.2% of the organic pollutants to be detained. The average of effluent wastewater contamination of the filter was 22 mg O2 LE-1. In the filter with dolomite chippings media can be cleaned wastewater with pollution reaches 500 mg O2 LE-1. The maximum load of organic pollutants is 14 mg O2 LE-1. The filtration path length to ensure wastewater cleaning up tolerance 0.8 m. In the filter with dolomite chippings media Ptotal is cleaned even 87.0%, Ntotal only 13.0% efficiency.