Thermal dehydration of urban biosolids with green liquor dregs from pulp and paper mill

Rehabilitation of Disturbed Lands with Industrial Wastewater Sludge

Wastelands of the mining industry are among the largest of disturbed areas that demand revitalization. To reduce environmental impact and to better manage these geo-resources, the formation of sustainable plant and soil complexes and the restoration of self-recovery soil function are critical points. The successful return of vegetative cover at post-mining sites requires eliminating the deficiency of organic matter. For this, we assessed the usability of non-traditional ameliorants to provide a better understanding of benefits from mutual dependencies of environmental resources. To prevent losses and to close resource cycles, we studied the applicability of wastewater sludge from the pulp and paper (SPP) industry as an amendment to counteract soil degradation and rehabilitate human-disturbed lands. Waste rock limestone, beresite, and phosphogypsum substrates of post-mining sites were used in vitro for the application of sludge and peat mixture and consequent grass seeding. The formed vegetative cover was analyzed to compare the germination and biomass growth on reconstructed soils. We assessed the efficiency of ameliorant combinations by two approaches: (1) the traditional technique of cutting-off plant material to measure the obtained plant biomass, and, (2) digital image analysis for RGB-processed photographs of the vegetative cover (r2 = 0.75–0.95). The effect of SPP on plant cover biomass and grass height showed similar results: land rehabilitation with the formation of a 20 cm soil layer on mine waste dumps was environmentally suitable with an SPP:soil ratio of 1:3. However, excessive application (ratio 1:1 of SPP to the soil) negatively affected seed germination and plant vegetation.

Beneficial use of lime mud from kraft pulp industry for drying and microbiological decontamination of sewage sludge

Sewage sludge (SS) is a global environmental, social, and economic problem that requires a sustainable management approach. Still, the production of other industrial wastes, such as lime mud (LM), has recently gained considerable attention to avoid landfilling. This work aims to present a new approach for converting SS and LM into value-added products within the circular economy perspective. In particular, the effect of LM and calcined lime mud (CLM) as drying adjuvants and SS sanitation agents are investigated. Two out of three SS samples show Escherichia coli contamination above the Portuguese limit established for soil application, while no Salmonella spp. was detected in the searched samples. The addition of CLM to SS in a ratio between 0.05 and 0.15 g CLM/g_wb, lead to complete elimination of the microbiological contamination in almost all cases. Contrarily, the use of LM does not seem efficient to act as a sanitation agent. Both LM and CLM show a positive impact on the drying process when compared to the raw SS, increasing the drying rate, and reducing the drying time. The most favourable drying conditions to maximize the drying rate and minimize the drying time (until 30% of moisture) are 130 °C, 0.15 g adj/g_wb, and 2.5 mm of plate thickness. The thermal treatment (100 and 130 °C) without adjuvants reduces the microbiological contamination below the legal limit. Overall, a beneficial effect is observed by adding CLM to SS, open the possibility of producing a safer organic soil improver.

Inorganic Waste Generated in Kraft Pulp Mills: The Transition from Landfill to Industrial Applications

Kraft pulp mills produce the main raw material for paper, while several waste products are generated in large quantities in the process. This review study addresses four of the main inorganic wastes formed by this industry, namely green liquor dregs (GLD), slaker grits (SG), lime mud (LM) and boiler fly ash (BFA), which are still mostly discarded in landfills. A brief overview of a typical industrial process was included to outline the waste generation points. The main chemical and physical properties are indicated for highlighting the most relevant characteristics to determine which applications may be considered in each case. An in-depth literature review allowed the identification of the main applications that have been tested mainly at the laboratory scale and some at an industrial scale. The applications are grouped into construction materials, geotechnical, environmental, agricultural and others. This assessment shows that the circular economy and the sustainable development goals of the UN are important issues for organizations in general, and the pulp mill in particular. In fact, this industry has managed to close the chemicals loops, recover energy and reduce water consumption in the process. However, the current situation of inorganic waste can still be improved if industrial applications are developed to avoid landfill.

Santos C, M. Matos A, Cardoso O, J. Quina M. Effect of Thermal Drying and Chemical Treatments with Wastes on Microbiological Contamination Indicators in Sewage Sludge

This work aims to evaluate the microbiological contamination of sewage sludge (SS) collected in urban wastewater treatment plants (WWTP) from Portugal. Two types of SS were considered: urban mixed (UM) and from anaerobic digestion (AD). The two types of samples were characterized in relation to the main physical and chemical parameters, as well as the microbiological contamination (Escherichia coli and Salmonella spp). Then, sanitation tests were conducted through thermal drying and chemical treatments. Towards a circular economy, industrial alkaline wastes (green liquor dregs - GLD, lime mud, coal fly ash, eggshell) were tested as alternatives to lime. Only six out of nineteen samples complied with the legal limits for both microorganisms. However, drying at 130 °C sanitized selected samples below the E. coli limit, regardless of the initial moisture or contamination. Additionally, CaO (obtained from eggshell) led to the complete elimination of E. coli at any dosage studied (0.05–0.15 g/g SS_{wet basis}). GLD evidenced the ability to reduce E. coli contamination at room temperature, but not enough to comply with the legal limit. In general, this work highlights the need to sanitize the SS before its application to the soil, and the positive role of some wastes on this goal.