Energy Recovery from Sewage Sludge: The Case Study of Croatia

Abstract

Croatia produced 21,366 tonnes of dry matter (DM) sewage sludge (SS) in 2016, a quantity expected to surpass 100,000 tonnes DM by 2024. Annual production rates for future wastewater treatment plants (WWTP) in Croatia are estimated at 5.8–7.3 Nm3/people equivalent (PE) for biogas and 20–25 kgDM/PE of sewage sludge. Biogas can be converted into 12–16 kWhel/PE of electricity and 19–24 kWhth/PE of heat, which is sufficient for 30–40% of electrical and 80–100% of thermal autonomy. The WWTP autonomy can be increased using energy recovery from sewage sludge incineration by 60% for electricity and 100% of thermal energy (10–13 kWhel/PE and 30–38 kWhth/PE). However, energy for sewage sludge drying exceeds energy recovery, unless solar drying is performed. The annual solar drying potential is estimated between 450–750 kgDM/m2 of solar drying surface. The lower heating value of dried sewage sludge is 2–3 kWh/kgDM and this energy can be used for assisting sludge drying or for energy generation and supply to WWTPs. Sewage sludge can be considered a renewable energy source and its incineration generates substantially lower greenhouse gases emissions than energy generation from fossil fuels. For the same amount of energy, sewage sludge emits 58% fewer emissions than natural gas and 80% less than hard coal and fuel oil. Moreover, this paper analysed the feasibility of sludge disposal practices by analysing three scenarios (landfilling, co-incineration, and mono-incineration). The analysis revealed that the most cost-effective sewage sludge disposal method is landfilling for 60% and co-incineration for 40% of the observed WWTPs in Croatia. The lowest CO2 emissions are obtained with landfilling and mono-incineration in 53% and 38% of the cases, respectively.

Using Sewage Sludge Ash as an Efficient Adsorbent for Pb (II) and Cu (II) in Single and Binary Systems

“…Twenty-seven European Union countries generated more than 11.5 million tons of sewage sludge in 2015, and this quantity is expected to increase up to 13 million tons by 2020 due to industrialization and urbanization [2][3][4][5]. In the past few years, European Union promoted the ecological management of such wastes by introducing directives regarding sewage sludge management and therefore classical methods, such as storage, are being replaced by methods leading to waste stabilization and safe recycling.…”

Waste activated sludge treatment in an anaerobic dynamic membrane bioreactor at varying hydraulic retention time: Performance monitoring and microbial community analysis

“…In addition, the efficiency of sludge bioconversion is low because of flocculation that hinders microbial degradation 7 . Current disposal techniques such as incineration, landfill, and agricultural usage have been discouraged, as they impact public health and the environment 8,9 . Instead, anaerobic digestion has become increasingly important as an economic and sustainable solution for sludge reduction and stabilization because of its efficient organic matter reduction and the possibility of energy recovery from the generated biogas 10 .…”

“…7 Current disposal techniques such as incineration, landfill, and agricultural usage have been discouraged, as they impact public health and the environment. 8,9 Instead, anaerobic digestion has become increasingly important as an economic and sustainable solution for sludge reduction and stabilization because of its efficient organic matter reduction and the possibility of energy recovery from the generated biogas. 10 However, the low organic loading rate often leads to inferior treatment performance of sludge digesters.…”

Stimulation of Lipid Extraction Efficiency from Sewage Sludge for Biodiesel Production through Hydrothermal Pretreatment

“…However, in recent years sewage sludge has gained attention as a promising source for biofuel production [3]. Many studies have suggested anaerobic digestion or fermentation and the direct use (through incineration after drying) of sewage sludge [4], but the low biological conversion efficiency and high energy consumption during sewage sludge drying are drawbacks of these methods. Recently, the high lipid content of sewage sludge has been gaining worldwide attention as a possible feedstock, owing to its low cost and availability, as it is an abundant organic waste [5].…”