Use of solar energy increases every year. In Latvia, solar energy is used mainly by solar collectors. The main part of the solar collector is the absorber, but not less important is the covering material which protects the absorber from the cooling impact of the wind. This cover must be transparent for solar radiation, but opaque for thermal radiation of the absorber, which is at greater wavelengths. Therefore it is important to measure absorption spectra of possible covering materials at visible and infrared wavelength ranges. Absorption spectra have been measured for several materials: glass, polythene, Plexiglas, and cells Plexiglas. Absorption spectra for all these materials are measured in three ranges: ultraviolet – visible (UV – VIS): 250 – 1000 nm; near infrared (NIR): 700 – 110 nm; infrared (IR): 1200 – 8000 nm. UV-VIS spectra with the ‘Ocean Optics’ device HR-4000 have been measured, but NIR and IR – with ‘Bruker’ Furje spectrometer EQUINOX 55. Evaluation of absorption spectra showed that the most suitable material (from the considered) for covering of solar collectors is Plexiglas.

As worldwide trends are changing gradually and sustainable resources economy and reduction of hazardous emissions are coming to the forefront, several industry sectors are forced to revalue their resource consumption. The main emphasis is currently placed on the recycling of by-products. One of the methods, definitely, includes burning of by-products to generate power, however it is not always the most efficient one. By-products must be used in the manner that ensures that they provide high added value for the operation of the company and are environmentally friendly. This research focuses on the use of the by-products of birch (Betula) veneer manufacturing, in order to obtain thermal insulation material. The following characteristics of the wood fibre insulation material were determined: thermal conductivity, water absorption, vapour permeability, and prototype reaction to fire. The characteristics of the obtained wood fibre thermal insulation material: thermal conductivity 0.038 W•mE-1•kE-1; water absorption 12 kg•mE-2; the conformity of the material even to D fire reaction class was not determined. The principal conclusion: the wood fibre thermal insulation material conforms to the requirements set for thermal insulation materials.

Superabsorbents are hydrophilic polymers that can absorb large amounts of water. These studies show that the use of superabsorbent may significantly reduce the negative effects of drought stress on plants. However, their use in the field cultivation has so far been minimal. The price of hydrogels has recently decreased significantly. This was the reason for starting research described in this work, in which the experimental plant was the winter wheat cultivar ‘Lucullus’ – the cereal which is the most intensively cultivated in Poland. The field experiment was conducted in the years of 2014 – 2016, in the Agricultural Experimental Station (AES) in Osiny, Poland, in 4 repetitions. TerrahydrogelAqua was evaluated in the following doses: 1) control without hydrogel, 2) 10, 3) 20 and 4) 30 kg•haE-1. Before harvesting, the plant samples were taken to determine the yield structure elements. After harvesting, grain yield at 15% moisture content was determined. The influence of hydrogel on winter wheat grain yield varied in individual years. On average, the yield of wheat grain from the treatment with a dose of 30 kg•haE-1 of hydrogel was significantly higher than from the control treatment or the treatment with a dose of 10 kg•haE-1 of hydrogel. The mean values of yield structure features, i. e. ear grain yield and weight of thousand grain were the highest at the dose of 30 kg•haE-1 of hydrogel. The effect of hydrogel on the average number of plants and ears per unit area and on the number of grains per ear was not found.

In the process of biological wastewater treatment, P-removal is efficient enough when the concentration of organic pollutants according to BOD5 (biochemical oxygen demand) is no higher than 190 mg lE-1 of O2 and its relationship with phosphorus does not exceed 20. Having studied the composition of wastewater from dairy farms it was determined that wastewater pollution according to BOD5 is from 800 to 900 mg lE-1 of O2 and the ratio of BOD5/Ptotal is 30-36. The paper gives the results of the tests on P-removal from wastewater carried out in a laboratory model. During investigations wastewater was flowing via mineral filters (filtralite P (FLP), zeolite (CE), and shulgite (SG)). Total amount of Ca, Fe and Al oxides contained in those filters were 23.0, 16.1 and 7.9% respectively. The rates of P-removal from wastewater in the filters were as follows: 88.5% (FLP), 45.5% (CE), and 96.3% (SG). Considering different hydraulic load, P-mass balance was calculated. The calculation results showed the following P absorption amounts: FLP - 5.08 g dE-1, CE - 1.76 g dE-1, and SG - 3.91 g dE-1 (calculated for 1 m**3 of each filter). Wastewater filtration through mineral media resulted in the removal of other pollutants, too: organic pollutants removal (according to BOD5) was 30.8 to 72.5%, and the removal of nitrogen compounds (more than 90% of which were in the form of ammonium salts) was even 93.2% in CE filter.

This paper describes the use of Scots pine (Pinus sylvestris L) bark humus and fine fractions for animal litter pellet manufacture, and the efficacy of various additives in improving absorbency. In Latvia is no researches about litter pellet manufacture of pine bark, and possibilities of increasing water absorbency; in internationals research papers there is also no information about the possibilities of improving water absorbency of pine bark pellets with various additives. The additives tested were fresh and fallen leaves, tree needles, dried hogweed and sawdust. Pellets were manufactured with a ZLSP200B granulator at Adazi city, Latvia, in 2014. The results indicated that production of small diameter pine bark pellets could be problematic. Absorbency of the pellets was tested both by rinsing and soaking the pellets, and results were compared to woodchip particle litter pellets. It was found that the best absorbency was achieved with adding up to 30% sawdust, which increased pellet absorbency both by rinsing and soaking. The results indicate that it is possible to manufacture pellets using Scots pine (Pinus sylvestris L.) bark humus and fine fraction with good absorbency which can be disposed of in sewerage systems.