The aim of this research is to work out the graphic method for the calculation of the maximum rain intensity with a different guarantee in Riga. In order to develop this method analysis as regards the rainfall rates having a different probability was carried out. The measurement data of maximum rainfall minute intensity (mm minE-1) 3 and 9 hours as well as daily common rainfall from the accessible archive materials in the period 1954-2006 have been studied in this research and treated with the mathematical statistics methods. After the data collection and calculations, the final results are shown in a graphical way in which it is easy to determine which guarantee percent and repetition probability the rain intensity in Riga may be foreseen. In order to determine which module of one factor regression is the most accurate, five different modules were investigated. From the modules studied the most adequate one for data analyses was the logarithmic module having the accuracy up to 92%. The analysis of the rainfall data as well as the research of the situation of the location place can help to choose the system of rain accumulation and infiltration for each building location thus improving the operation of the total sewerage system. The calculations may be useful in practice to calculate the runoff rates from the areas of different covering. If necessary, using the graphic, it is possible to work out a mathematical expression for the calculation of the maximum rain intensity having any necessary probability. The accessibility and application of a wide range of materials for modern surfaces or infiltration buildings in the world present a wider range of their practical use for separate modern solutions in Riga.

The human influence on hydrological cycle has created many surface problems in the Riga city. Rainfall amount increases year after year as a result of global warming and bad water exchange. Solid covering of squares and greened areas is one of the most significant results of urban development causing larger rainwater runoff from the territories and calling for the necessity to drain rain water rapidly in a short time. This phenomenon is observed in the last years due to the fast construction development and simultaneous expansion and improvement of streets and court yards. The main problem matter is the still existing old sewage co-system which encounters difficulties to work with full capacity during long term rainfall. Thus justifiable steps have to be taken in order to discover new engineering solutions to prevent overflow of streets in Riga during rains. To enquire into the matter, rain intensity in Riga, influence of rainwater on streets, overflowing of collectors, and operation of pumping stations are studied in this paper. Rain intensity measurements during 1980-2006 in Riga have been aggregated. As acquired data shows, maximum rain intensity was observed on July 30 of 2005 when the rainfall was 49.4 mm during a 3-hour time, which caused overflowing of some streets, collectors, and pumping stations. Data on local and main pumping stations at the right bank of the river Daugava during various rainfalls suggest that pumping stations start to overflow during enduring rainfalls, 1-3 hours long and with average intensity of 0.1-0.4 mm minE-1 (Ziemelnieks, Tilgalis, 2008). Data gathered indicate, that it is necessary to separate sewage systems for everyday necessities from those for rainwater.

The aim of this research is to study the separation possibilities of household and rainwater sewage collectors in Riga. The performance of sewage pumping stations on the right and left banks of the Daugava River during the dry periods and those of rainfall is analyzed as well as the yearly costs of electric energy are given. This paper analyses the costs that would rise with re-building of the central regional co-system into the separated one. The locations are shown where the rainwater collectors are connected to the household sewage collectors likewise the recommendations are given for the separation of these collectors.

Pollution and treatment efficiency of surface (rain) wastewater, forming in the production territory of meat processing company LTD ‘Krekenavos mėsa’ (centre of Lithuania in Kėdainiai district), were investigated in the period 2004-2009. On the surface of the company territory the precipitation water turns to surface wastewater, which is collected and sent down to treatment equipment. Wastewater samples were taken before and after biological treatment. The samples were investigated in the Chemical Analysis Laboratory of the Water Research institute of Lithuania University of Agriculture certified by the Environment Ministry of the Republic of Lithuania The following indices have been determined: biochemical oxygen demand (BOD7) – by titrometric method, suspended solids (SS) – by gravimetric method, having filtered the substance through a mid-thickness filter. Concentrations of oil pollutants were determined with the help of a spectrophotometric device of infrared rays IKAN-1 in the Analytical Department of Agrochemical Study Center of Lithuanian Agricultural Institute. During six years of investigation average wastewater pollution with suspended materials was 35.0 mg LE-1, which by 14% exceeded the BAC. Suspended solids determined BOD7 concentrations in surface wastewater by 46%. The best treatment effect was received in the purification of oil products - 96%, suspended solids - 60%, organic pollutants - 59%. The wastewater discharged from the company production territory to natural environment was clean as concentrations of the investigated oil hydrocarbons, biochemical oxygen demand and suspended solids in the surface wastewater were 26, 4 and 2 times respectively lower than biggest available concentration.

Modelling of the domestic wastewater treatment and removal of the Ptotal in the vertical filters with the sand, dolomite powder and dolomite chippings each separately used as a filter media was performed. Six filter models taking 0.2 m2 each were installed. The length of the filtration path was equal to 0.8 m in three of these models and 0.4 m in the other three models. The hydraulic load on the filters was equal to 0.03 m3 mE-2 dE-1 in 2008, and it was equal to 0.06 m3 mE-2 dE-1 in 2009. The domestic wastewater which had undergone the pre-cleaning in the septic systems was poured into the models. Their average pollution with the Ptotal reached 14.6 mg LE-1 in the first year and 9.2 mg LE-1 in the second year. When the filtration path was equal to 0.8 m and the hydraulic load was equal to 0.03 m3 mE-2 dE-1, the Ptotal was removed from the wastewater with the efficiency of 99.9% in the dolomite powder filter. In the filter models with the sand and dolomite chippings, the Ptotal was removed with the same efficiency of 87.7%. When the hydraulic load doubled, the efficiency of P removal decreased to 59.8% in the sand filter and down to 45.7% in the dolomite chippings filter. When the hydraulic load reached 0.06 m3 mE-2 dE-1, only the dolomite powder filter could ensure the adequate cleaning of the domestic wastewater up to the allowable norms.

In 2003 an experimental model of the dairy waste water cleaning facility was equipped for cleaning the wastewater of the milk collection station. We examined the possibilities to destruct the organic pollutants present in the dairy wastewater in the sand filters of vertical and horizontal filtration. The pollution level of the dairy wastewater is from 2 to 4 times higher than that of the domestic wastewater. The dairy wastewater was cleaned following the procedure: cleaning in the aeration-flocculation system-cesspool-two stage sand-reed filter. The pollution of the wastewater leaving the cleaning facility never exceeded the allowable norms. The average BOD5 was 4 mg O2 LE-1 and the maximal value was 9.6 mg O2 LE-1. The investigation revealed that the horizontal sand-reed filter with the filtration path of 7 meters ensured cleaning of the dairy wastewater up to the allowable norms. The organic pollutants were cleaned with the efficiency of 97.2% after filtration through such a sand layer. In order to find out the possibilities of vertical filtration filters use for cleaning the dairy wastewater leaving the milk collection stations, we performed a modelled investigation. The wastewater cleaning efficiency in respect to BOD5 reaches 99.3% in these filters. The calculation according to the regression equation received showed that filtration through 0.6 m sand layer ensured successful cleaning of the wastewater up to the allowable norms. In such a vertical filtration filter the average BOD5 cleaning level was 20 mg O2 LE-1.

Surface water runoff, formed in the company areas due to changing wastewater discharge and pollution fluctuations can be treated in retention ponds. Pollutants, released into the ponds, mineralize during complex natural biochemical processes in the aquatic environment. The paper presents the long-term observation data (2004 – 2016 m.) on the purification of surface wastewater, formed in the company’s production territory, in retention ponds. The aim of this work is to identify surface wastewater purification efficiency in retention ponds. Wastewater samples were taken before and after biological treatment. The samples were investigated in the Chemical Analysis Laboratory of the Water Research Institute of Lithuania University of Agriculture. Biochemical oxygen demand (BOD7 ) was determined with titrometric method, suspended solids (SS) – with gravimetric method, having filtered the substance through a mid-thickness filter. Concentrations of oil pollutants were determined with the help of a spectrophotometric device of infrared rays IKAN-1 in the Analytical Department of Agrochemical Study Center of Lithuanian Agricultural Institute. Although the suspended solids, BOD7, and oil hydrocarbon concentrations, released into the natural environment, were below the MAC when they are collected from the company’s production areas, they are often contaminated; therefore, it is necessary to treat them. The purification efficiency of researched materials was satisfactory and reached 61, 64 and 91%.

Eutrophication caused by water pollution with nutrients (nitrogen (N) and phosphorus (P)) is one of the main environmental problems nowadays. Poor water quality might be caused by many natural and anthropogenic factors. The most common anthropogenic factors are water pollution caused by intensive agriculture (e. g. intensive fertilizer use, high density of livestock) and discharges from municipal waste water treatment plants (WWTP). In this study, nutrient load from WWTP to the River Berze basin in time period from the year 2005 to the year 2015 was described. In total, 23 WWTPs of the study area were analysed using descriptive statistics to calculate average values of nutrient amount and concentrations discharged to River Berze basin. From 2005 to 2015 average N and P load from WWTP to the River Berze basin have been reduced, but concentration of N and P in treated wastewater (WW) have increased. The largest WWTP of the study area – Krigeri (WWTP of city Dobele) is subject to the regulations of treated WW quality set by Republic of Latvia Cabinet Regulation No. 34. The WWTP Krigeri meets the regulations, but overall situation in the study area suggests that strict control of smaller WWTP should be made.

Main factors raised interest about biomass as the source of energy increase renewable resource demand in the context of Green house gases emissions decrease and the problem of environmentally friendly and efficient waste utilization. Legislation of waste water sewage sludge use is becoming stricter now. After cutting away top peat layer of peat quarry, the owners have two alternatives: the first, to flood the fields and transform them into bogs, the second, to carry out some economic activities - one of which must be field afforestation with traditional or fast growing tree species. Before planting trees it is necessary to fertilize the fields, and waste water sewage sludge will be one of potential fertilizers. Aims of research were to determine the impact of waste water sewage sludge fertilization 10 t haE-1 on tree growth and soil properties. Concentration changes of N, P, K, and Ca, Mg in different depth and concentration of S and total C and heavy metal in soil top layer during the year 2006 were determined. The effect of fertilization on tree growth and stock was determined by the non-destructive method, data were calculated by height and root core diameter of trees. Fertilization stimulates tree growth as weed growth too. On peat areas observed soil acidity decreasing. Despite of sufficient amount of nutrients willows were not suitable for peat fields. To avoid increasing of heavy metals content in soils, only qualitative waste water sewage sludge or waste water sewage sludge composts is acceptable for fertilization.

The objective of the present studies has been to estimate peculiarities of nitrogen removal in constructed wetlands of different construction. In limited companies (LTD) 'Pastoge' and 'Nikola', constructed wetlands of vertical flow (VFCW) are arranged, while limited company (LTD) 'Agaras' has two-stage constructed wetlands of horizontal flow (HFCW). In all the objects the supplied wastewater is after primary treatment. Having compared the efficiency of ammonium and nitrite nitrogen removal in two types of constructed wetlands (VFCW and HFCW) it was determined that larger amounts of total nitrogen are removed in HFCW (38.1%) rather than in VFCW (24.4%). However, in VFCW smaller amounts of ammonium and nitrite nitrogen are discharged with wastewater. No significant effect of the fluctuations of ambient temperature on the removal of ammonium and nitrite nitrogen was observed in HFCW (difference in average values of cold and warm periods was 3-8%). A rather reliable relation (R2 = 0:738) was determined between ammonium nitrogen concentrations in wastewater outflow and HFCW load according to total nitrogen, however, ammonium nitrogen amounts in treated wastewater (when filter load according to total nitrogen is 0.3 to 4.6 g mE-2 dE-1) exceeded the maximum allowable concentration (MAC) and were fluctuating from 6 to 32 mg lE-1.