•The firing temperature of sewage sludge ash (SSA) affects the brick properties.•The best results were obtained with mixed-in SSA fired at 900 °C.•The soluble salts level rises with SSA addition but ...remains within allowed limits.•Higher firing temperatures reduce the soluble salts level in the bricks.
The influence of combustion temperature on the properties of sewage sludge ash (SSA) as a substitute material for the production of fired clay bricks was studied. The experiments were performed with sewage sludge (SS) from wastewater treatment plants (WWTP) in Zagreb (ZG) and Karlovac (KA). SS samples were fired at temperatures of 800, 900 and 1000 °C, and the properties of the resulting SSA were determined and compared with clay and SS. Bricks with 5 wt% SSA as clay substitute were prepared and compared with clay bricks (control). SSA bricks produced at higher temperatures are of higher strengths and lower water absorption, which are both desirable properties. Compressive strength tests showed that SSA obtained at a firing temperature of 900 °C is the most suitable for use in bricks. For the first time, the influence of SSA on the content of soluble salts in bricks was tested. The content of soluble salts, expressed by the electrical conductivity of leachate, in SSA bricks showed increased values compared to the control bricks, which were 2.8 and 4.6 times higher in bricks with SSA produced at 800 °C. Still, bricks with SSA prepared at higher temperatures had lower content of soluble salts and also SSA from KA had lower soluble salts content than SSA from ZG. The total amount of Na+, K+, Mg2+ in all bricks made with SSA was below the limits for category S2 according to EN 771-1.
Quantities of sewage sludge that are thermally treated (mostly incinerated) are increasing, resulting in growing quantities of sewage sludge ash (SSA) which also requires further management. Despite ...its potential as a resource, it is still largely landfilled. Considering the presence of potentially toxic and hazardous heavy metals in SSA, this paper analyzes how the change in the leaching concentrations of the selected heavy metals from landfilled SSA impacts the environment (air, water, and soil) by the means of LCA. When considering human toxicity potential as impact category, dominant impacts were due to emissions into the air, primarily caused by leaching of selenium and somewhat less cadmium, mercury and nickel. Mercury had a dominant impact when considering the terrestrial ecotoxicity potential impact. In the SSAs obtained from Croatian sludge, molybdenum leaching, along with selenium and mercury, showed a dominant impact. Therefore, due to the high variability of trace elements, detailed analysis of different SSAs is needed.
The aim of this paper is to analyse sewage sludge production at the level of Medimurje and Varazdin counties with economic analysis of acceptable technical/technological solutions for sludge ...management routes. The topic is very broad, so the focus was placed on four variants of sludge disposal, which were determined by preliminary analysis to be the most applicable for the area in question. These are: 1) disposal of sewage sludge in agriculture, 2) incineration of sludge in a central mono-incinerator, 3) composting for the area of Varazdin County and at the same time use of sludge reed beds for the area of Medimurje County, and 4) export of sludge outside the state borders. Based on the analysis carried out for the described four variants, sludge incineration in a regional mono-incinerator turned out as the economically most advantageous solution, while the variant that includes disposal of sludge in agriculture has showed as the most expensive one. The last one also showed the largest range of costs uncertainties, but the mentioned facts are greatly influenced by unfavourable legislation, the changes of which in a more rational direction would greatly contribute to the greater competitiveness of this variant. Overall, taking into account the lowest cost and uncertainties in the predicted unit costs, the sludge composting in the Varazdin County and the construction of a reed beds for the Medimurje County, turned out to be the optimal variant. This solution is also the one that was ultimately adopted in practice.
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.
The wastewater treatment plant Varaždin upgrade project envisages the reconstruction of the rain overflow directly upstream of the plant. Physicochemical parameters of water quality (Biological ...Oxygen Demand, Chemical Oxygen Demand, Total Nitrogen, Total Phosphorus, Suspended Solids) in sewage/drainage system and in the accumulation were analyzed. In accordance with expected values of concentrations in overflow and in the accumulation, an analysis of the water quality in the accumulation after mixing was performed with certain assumptions. The results show that the ecological condition of the accumulation generally remains unchanged, classified as good condition, except for Chemical oxygen demand which is a critical parameter. Paper refers to the frequency and duration of possible exceedances of the Chemical oxygen demand limits and gives critical analysis of the realistically expected impacts. A proposal for conducting more detailed analysis with a larger database and by modelling pollution discharge by a complex three-dimensional model is given.
Electrochemical wastewater treatment technologies are increasingly being used in practice, and the combination of electrocoagulation with advanced oxidation processes has been shown to increase ...treatment efficiency. The treatment of oily wastewater produces electrocoagulated metal sludge (EMS). In this work, the possibility of using different ratios of EMS produced during oily wastewater treatment was investigated. EMS was dried conventionally in an oven at 105 °C and used as a partial substitute for clay in the manufacture of laboratory bricks. The main research objectives of this study were to examine the possibility and justification of introducing EMS in brick production. The results show that an increase in the proportion of EMS in the manufacturing of bricks leads to a deterioration in the quality of the bricks. Bricks with an addition of 1 wt% and 5 wt% EMS showed the best properties. The loss on ignition (LOI), compressive strength, boiling water absorption and initial water absorption were determined at 5.7%; 49 N/mm2, 16%, 14 g/min/200 cm2, 15% for modified bricks with 1 wt% EMS and 6.3%, 48 N/mm2, 20%, 15 g/min/200 cm2 for modified brick with 5 wt%.
Wastewater containing oil is becoming a growing problem worldwide due to increasing quantities and existing pollution. The pollutants contained in these effluents, when released into the environment, ...affect surface and groundwater pollution, endanger human life and health, and pollute the atmosphere. Their sustainable treatment should be cost-effective and meet all requirements to prevent the pollutants from being transferred to the environment or to humans. This study gives a brief overview of some conventional and modern technologies that have been proven in practice for the treatment of oily wastewater. Due to the high concentrations of chemical oxygen demand (COD) and total hydrocarbons (mineral oils) in oily wastewater its treatment is complex, and to achieve optimum treatment conditions and efficiency a combination of different technologies is required. This paper focuses on hybrid electrochemical process combining the electro-Fenton process (EF) using stainless steel (SS), and electrocoagulation (EC) with iron (Fe) and aluminum (Al) electrodes. The influence of the two different types of pretreatment, i.e., pretreatment of the raw wastewater on the overall efficiency of oily wastewater treatment using a hybrid treatment process, which is a combination of AOP and EC, is investigated. Two type of pretreatment were tested, with primary sedimentation and pretreatment of the mixture of raw wastewater and previously generated electrochemical sludge with primary sedimentation. During the applied treatment processes, the concentration of COD, mineral oils, and other elements in the raw and treated wastewater (As, Ca, Cd, Cr, Cu, Ni, Pb, Sn, Zn) and in the generated sludge (K, Ca, Fe, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, As, Br, Rb, Sr, Y, Zr, Pb, Th) were determined. By combining the primary sedimentation of the raw wastewater with the EF/EC process, a mineral oil removal efficiency of 72% (1.1 mg/L) and COD of 89% (170 mg/L) was achieved. Using primary sedimentation of a mixture of raw wastewater with previously generated sludge as pretreatment and followed by EF/EC treatment, a higher efficiency for mineral oils of 94% (7.6 mg/L) and COD of 98% (43 mg/L) was achieved.
The gasification of sewage sludge (SS) was studied in a semi-industrial pilot plant consisting of a rotary kiln reactor. The gasification process was preceded by drying the SS in an integrated ...tubular rotating structure with built-in worm conveyors, to increase the dry matter (DM) content in the SS (> 90 wt.%). The released hydrogen-rich syngas from the gasification process of SS had low heating value (LHV) of approximately 8.83 MJ N.sup.-1 m.sup.-3 (equal to 2.45 kWh N.sup.-1 m.sup.-3) due to the high content of combustible gases H.sub.2 (41.5 vol.%) and CH.sub.4 (3.2 vol.%). Also investigated was the incorporation of sewage sludge ash (SSA) generated in the process of gasification as a partial substitute for clay in the production of clay bricks. Amounts of 5 wt.%, 10 wt.%, 20 wt.% of clay were replaced by SSA. By incorporating SSA at 5 wt.%, the new brick product achieved 4.5% higher compressive strength compared to the control brick. Keywords: sewage sludge, gasification, syngas, sewage sludge ash brick production, circular economy
Effluent transport in the aquatic environment can be described by using very complex mathematical formulations that include the most relevant processes and their unsteadiness and non-uniformity. This ...paper gives some evidence of the capability and importance of numerical modelling implementation in the analysis of effluent transport, following the discharge from sewerage submarine outfalls. Numerical models Cormix, Mike 21fm, Mike 3 fm and ROMS are described in brief and applied to a particular example in the vicinity of the city of Porec. Five separate sewerage systems and associated submarine outfalls were encompassed within the numerical model spatial domain: Lanterna, Cervar-Porat, Porec north, Island Sv. Nikola, Porec south, Petalon i Koversada. Two scenarios of effluent treatment and discharge are modelled that represent the present and the future-planned state according to the development concept project. Positive aspects from the planned activities are obtained through comparison between the faecal coliforms concentration dynamics.Original Abstract: Pronos oblaka zagadenja u morskim akvatorijima moze se opisati izuzetno slozenim matematickim operacijama, koje ukljucuju veliki broj utjecajnih cimbenika te njihovu nejednolikost i nestacionarnost. U radu su prikazane mogucnosti i vaznost koristenja razlicitih matematickih modela pomocu kojih se na ucinkovit i relativno brz nacin moze dobiti realna slika pronosa zagadenja iz podmorskih ispusta. Opisani su sofisticirani matematicki modeli Cormix, Mike 21fm, Mike 3fm i ROMS, uz prikaz njihove primjene na konkretnom primjeru. Odabrano je podrucje Porestine uz ispitivanje utjecaja podmorskih ispusta sustava javne odvodnje Lanterna, Cervar-Porat, Porec sjever, Otok Sv. Nikola, Porec jug, Petalon i Koversada, na promjene stanja u morskom akvatoriju sireg podrucja. Razmatrana su dva slucaja, od kojih se prvi odnosi na sadasnji stupanj izgradenosti sustava odvodnje, a drugi ukljucuje sve planske promjene prema usvojenoj koncepciji razvoja. Kao osnovni pokazatelj kakvoce vode u efluentu usvojena je koncentracija fekalnih koliforma. Dodatno je razmatran i utjecaj bioloske razgradnje organske tvari.
The paper presents commonly used methodology for assessing damage of water supply networks after a seismic event. The methodology relies on deriving and applying so-called vulnerability function. An ...overview of the existing vulnerability functions is given together with parameters, primarily related to soil deformations, which are influencing the assessment. Also, a critical review of the possibility of their use is given. Finally, by using two approaches, the estimated number of damages, with associated repair costs, is given for the water supply network of the City of Petrinja after the earthquake on December 29, 2020. With a total of 3 800 new damages, it is estimated that the total repair costs are around HRK 28 million. The accuracy of these estimates should be verified after detailed collection and processing of relevant data in accordance with the given guidelines.
PDF
