a b s t r a c t EU import dependence on hydrocarbons and resulting negative environmental impact related to their use led to setting of new measures and energy policy that will make, in time, a post carbon society more feasible and achievable. Energy systems of this society will be based on four pillars: Renewable Energy, Buildings as Positive Power Plants, Energy Storage and Smart grids in combination with Plug-in Vehicles. All these pillars must be supported by the use of smart energy storage. The results of previous research has shown that in order to increase security, efficiency and viability, there is need for energy storage, in primary or secondary form, in order to transfer energy surplus from period of excess to the period when there is a lack. The problem of today's storage systems is that they increase the cost of already expensive, distributed and renewable energy sources. That makes the large scale use of storage systems even less economically viable in market circumstances, despite economics of scale. The paper shows results of an energy planning methodology applied to several cases where use of smart energy storage system helps integration of energy flows, transformations and energy demand at the location of the energy end-use or close to it. Main results presented in this paper focus on planning a 100% independent energy system of Croatia. They also show the role of energy storage in a self-sustainable energy system with excess electricity production from renewable energy sources. The technical and financial analyses have been carried out for periods of one year taking into consideration demands and renewable energy production during all hours.

The goal of this work is to find a solution for disposal of Vitroplast FR4, a material found in waste printed circuit boards. In this study, the influence of addition of Vitroplast, generated by mechanical treatment of printed circuit boards waste on concrete properties such as compressive strength was investigated in laboratory conditions. By substitution of filler (i.e. sand) in a mass ratio of 5, 10, 15 and 20% with Vitroplast in concrete mixture, the compressive strength decreased into 57.5, 84.5, 95.0 and 95.9%. The results of leaching tests have shown that by incorporating Vitroplast in concrete mixtures in a 10% mass ratio, the elution of arsenic and cadmium is below the limitations prescribed for inert wastes. The studied approach offers the possibility for environmental friendly recycling of printed circuit boards.

Polystyrene concrete, as a type of lightweight aggregate concrete, has been used in civil construction for years. The use of waste expanded polystyrene (EPS) as a fi ll material in lightweight concrete production is highly recommended from the point of view of the circular economy. Published data shows that an increase in the proportion of lightweight aggregates, i.e. EPS, results in a decrease in strength, bulk density and thermal conductivity of the concrete. Utilizing large quantities of waste EPS in non-structural polystyrene concrete production is particularly important. Unlike structural polystyrene concrete, according to the published papers, non-structural polystyrene concrete has not been investigated suffi ciently. The purpose of this paper is to determine the infl uence of the ratios of the basic components in a concrete mixture on the bulk density and compressive strength of non-structural polystyrene concrete produced by utilizing waste EPS as a fi ll material. The test specimens, i.e. cubes with an edge length of 100 mm each, were prepared in laboratory conditions by varying the proportions of EPS, sand up to 600 g and cement ranging from 300 g to 450 g per specimen. Bulk density and compressive strength were determined for the test specimens. Laboratory research results show a dependence of the component ratio on the bulk density ranging from 360 kg/m 3 to 915 kg/m 3 and compressive strength ranging from 0.385 MPa to 2.538 MPa.

Original scientific paper In the paper an experimental research has been carried out regarding the possibility for the use of incinerated sewage sludge ash (ISSA) in the production of cement mortars with partial cement replacement. Different mixtures of cement mortar have been investigated, with comparison of its basic characteristics with and without certain amounts of added ISSA that was incinerated at the temperature of 800 °C. Additionally, the influence of the additives (metakaolin and silicon dust) was also investigated with the purpose to improve the physical characteristics of mortars. Altogether 177 specimens of cement mortar were investigated, with 9 different mixtures. In this research the sewage sludge from the Zagreb wastewater treatment plant was used. Results have shown satisfying physical and mechanical characteristics of mortars with added ISSA (workability, setting time, flexural and compressive strength) which brings to conclusion that use of ISSA in production of cement mortars seems possible and justified.Keywords: cement mortar; incineration; ISSA; sewage sludge; wastewater Uporaba pepela dobivenog spaljivanjem mulja u proizvodnji cementnog morta: pilot projekt u Hrvatskoj Izvorni znanstveni članak U ovom radu je provedeno istraživanje mogućnosti i opravdanosti uporabe mulja s uređaja za pročišćavanje otpadnih voda na način da se pepeo dobiven spaljivanjem mulja ugrađuje u cementni mort kao sirovina (zamjena dijela cementa). U radu su provedena ispitivanja na cementnom mortu, pri čemu su razmatrane usporedbe osnovnih svojstava mješavina morta bez dodatka pepela i s dodatkom određenih udjela pepela dobivenog spaljivanjem mulja na temperaturi 800 °C. Dodatno je ispitivan i utjecaj dodatka aditiva (metakaolina i silicijske prašine), s ciljem poboljšanja fizikalnih karakteristika morta. Ukupno je proizvedeno i ispitano 177 uzoraka cementnog morta s 9 različitih mješavina. Za potrebe ovog istraživanja rabljen je mulj dobiven na uređaju za pročišćavanje otpadnih voda u Zagrebu. Dobiveni rezultati s dodatkom pepela pokazali su zadovoljavajuća svojstva što navodi na zaključak da je u pogledu ispitivanih svojstava (obradljivost, vrijeme vezivanja, čvrstoća na savijanje i tlačna čvrstoća) moguća i opravdana uporaba mulja u proizvodnji cementnog morta.

Effective wastewater purification in subsurface flow constructed wetlands must include adequate pretreatment and ensure a sufficient amount of dissolved oxygen. In a pilot-scale operation, a subsurface flow constructed wetland (CW) consisted of a primary settlement tank, a trickling filter for pretreatment and two serially assembled basins. The trickling filter was added to ensure sufficient aeration, increase purification of the wastewater and shorten the wastewater purification time. The estimated nominal flow was 0.7 m3/d. The experiments were conducted using the wastewater from the municipal sewage canal of the city of Zagreb, with utilization of three different flows: 0.72 (A), 1.44 (B) and 2.88 (C) m3/d. The efficiency of the purification process was monitored over a period of three years (TSS, BOD5, COD, NH4-N, NO2-N, PO4-P, dissolved oxygen, temperature and pH). The experimental results showed an increase in the removal efficiency with a doubling of the nominal flow from 0.7 to 1.44 m3/d, which could be related to the implementation of the trickling filter where high removal rates were achieved.