From municipal/industrial wastewater sludge and FOG to fertilizer: A proposal for economic sustainable sludge management

• Published in: Journal of environmental management 2016-12, Vol.183 (Pt 3), p.1009-1025
• Main Authors: Bratina, Božidar, Šorgo, Andrej, Kramberger, Janez, Ajdnik, Urban, Zemljič, Lidija Fras, Ekart, Janez, Šafarič, Riko
• Format: Article
• Language: English
• Subjects: Agriculture; Biofuels; Chitosan; Desiccation; Digestate; Fertilizer; Fertilizers; Fertilizers - economics; Heavy metals; Heavy metals' reduction; Incineration; Landfill; Magnetite Nanoparticles; Metals, Heavy - analysis; Metals, Heavy - chemistry; Metals, Heavy - isolation & purification; Nitrogen - analysis; Nutrient removal; Phosphorus; Potassium; Sewage - chemistry; Sludge; Sludge treatment; Sustainability; Waste Disposal, Fluid - economics; Waste Disposal, Fluid - instrumentation; Waste Disposal, Fluid - methods; Waste Water - chemistry; Wastewater sludge; Water treatment plants
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2016.09.063

After a ban on the depositing of untreated sludge in landfills, the sludge from municipal and industrial water-treatment plants can be regarded as a problem. Waste products of the water treatment process can be a problem or an opportunity - a source for obtaining raw materials. In the European Union, raw sludge and fats, oil and grease (FOG) from municipal and industrial wastewater treatment plants (WWTP) cannot be deposited in any natural or controlled environment. For this reason, it must be processed (stabilized, dried) to be used later as a fertilizer, building material, or alternative fuel source suitable for co-incineration in high temperature furnaces (power plants or concrete plants). The processes of drying sludge, where heat and electricity are used, are energy consuming and economically unattractive. Beside energy efficiency, the main problem of sludge drying is in its variability of quality as a raw material. In addition to this, sludge can be contaminated by a number of organic and inorganic pollutants and organisms. Due to the presence or absence of pollutants, different end products can be economically interesting. For example, if the dried sludge contains coliform bacteria, viruses, helminths eggs or smaller quantities of heavy metals, it cannot be used as a fertilizer but can still be used as a fuel. The objectives of the current article is to present a batch-processing pilot device of sludge or digestate that allows the following: (1) low pressure and low temperature energy effective drying of from 10 to 40% remaining water content, (2) disinfection of pathogen (micro)organisms, (3) heavy metal reduction, (4) production of products of predetermined quality (e.g. containing different quantities of water; it can be used as a fertilizer, or if the percentage of water in the dry sludge is decreased to 10%, then the dried sludge can be used as a fuel with a calorific value similar to coal). An important feature is also the utilization of low-pressure technology to prevent odorous gasses from spreading into the environment. There are presented two new technologies: a) Sewage sludge or digestate drying in the vacuum chamber consumes approx. 1 kWh/dm3 of evaporated water and, therefore, reaches a price of 180–240 Euros/t Dry Matter (DM), and b) Heavy metals' reduction using adsorbing reaction with magnetite nanostructures can decrease the level of heavy metals in the sewage sludge or digestate up to 20% in one cycle, which can be repeated several