Effect of sewage sludge composition on the susceptibility to spontaneous combustion

Revealing the role of microalgae-bacteria niche for boosting wastewater treatment and energy reclamation in response to temperature

Conventional biological treatment usually cannot achieve the same high water quality as advanced treatment when conducted under varied temperatures. Here, satisfactory wastewater treatment efficiency was observed in a microalgae-bacteria consortia (MBC) over a wide temperature range because of the predominance of microalgae. Microalgae contributed more toward wastewater treatment at low temperature because of the unsatisfactory performance of the accompanying bacteria, which experienced cold stress (e.g., bacterial abundance below 3000 sequences) and executed defensive strategies (e.g., enrichment of cold-shock proteins). A low abundance of amoA-C and hao indicated that conventional nitrogen removal was replaced through the involvement of microalgae. Diverse heterotrophic bacteria for nitrogen removal were identified at medium and high temperatures, implying this microbial niche treatment contained diverse flexible consortia with temperature variation. Additionally, pathogenic bacteria were eliminated through microalgal photosynthesis. After fitting the neutral community model and calculating the ecological niche, microalgae achieved a maximum niche breadth of 5.21 and the lowest niche overlap of 0.38, while the accompanying bacterial community in the consortia were shaped through deterministic processes. Finally, the maximum energy yield of 87.4 kJ L^-1 and lipid production of 1.9 g L^-1 were achieved at medium temperature. Altogether, this study demonstrates that advanced treatment and energy reclamation can be achieved through microalgae-bacteria niche strategies.

Thermal Susceptibility of Nickel in the Manufacture of Softeners

The chemical industry includes a wide range of factories focused on obtaining final products as: (i) plastics; (ii) chemical fibers; (iii) rubber; (iv) perfumery and cosmetic products; and (v) cleaning products. Although the level of safety in the activities and installations of this sector is very high, the use of dangerous substances implies an increased risk of suffering an accident involving the emission of hazardous substances, as well as endangering the safety of workers. In the case of the manufacture of softeners, the presence of isopropanol (C3H8O), and dimethyl sulfate (CH3)2SO4), have been reported to be the accident cause in most of the cases. The European accident database (eMars) reported an accident in which the presence of impurities of nickel (Ni) in the hydrogenated tallow used as raw material for softener production may have increased thermal reactivity and the chances of spontaneous combustion. This paper analyzes the results obtained with the Maciejasz Index (MI) to understand the thermal susceptibility of these substances in liquid state. The results show that combinations of nickel (hydrogenated tallow catalyst) with other liquid substances (isopropanol, dimethyl sulfate, and sulfuric acid) are not sufficiently reactive with oxygen to cause a spontaneous combustion.

Synthesis and evaluation of cationic flocculant P(DAC-PAPTAC-AM) for flocculation of coal chemical wastewater

In this study, a high-efficiency cationic flocculant, P(DAC-MAPTAC-AM), was successfully prepared using UV-induced polymerization technology. The monomer Acrylamide (AM): Acryloxyethyl Trimethyl ammonium chloride (DAC): methacrylamido propyl trimethyl ammonium chloride (MAPTAC) ratio, monomer concentration, photoinitiator concentration, urea content, and cationic monomer DAC:MAPTAC ratio, light time, and power of high-pressure mercury lamp were studied. The characteristic groups, characteristic diffraction peaks, and characteristic proton peaks of P(DAC-MAPTAC-AM) were confirmed by fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), ¹H nuclear magnetic resonance spectrometer (¹H NMR), and scanning electron microscopy (SEM). The effects of dosage, pH value, and velocity gradient (G) value on the removal efficiencies of turbidity, COD, ammonia nitrogen, and total phenol by poly aluminum ferric chloride (PAFC), P(DAC-MAPTAC-AM), and PAFC/P(DAC-MAPTAC-AM) in the flocculation treatment of coal chemical wastewater were investigated. Results showed that the optimal conditions for the flocculation of coal chemical wastewater using P(DAC-MAPTAC-AM) alone are as follows: dosage of 8-12 mg/L, G value of 100-250 s ^- 1, and pH value of 4-8. The optimal dosage of PAFC is 90-150 mg/L with a pH of 2-12. The optimal dosage for PAFC/P(DAC-MAPTAC-AM) is as follows: PAFC dosage of 90-150 mg/L, P(DAC-MAPTAC-AM) dosage of 8-12 mg/L, and pH range of 2-6. When P(DAC-MAPTAC-AM) was used alone, the optimal removal efficiencies of turbidity, COD, ammonia nitrogen, and total phenol were 81.0%, 35.0%, 75.0%, and 80.3%, respectively. PAFC has good tolerance to wastewater pH and good pH buffering. Thus, the flocculation treatment of coal chemical wastewater using the PAFC/P(DAC-MAPTAC-AM) compound also exhibits excellent resistance and buffering capacity.

Residuals, sludge, and biosolids: Advancements in the field

Advancements in the field of residuals, sludge, and biosolids have been made in 2019. This review outlines the major contributions of researchers that have been published in peer-reviewed journals and conference proceedings throughout 2019 and includes brief summaries from over 125 articles. The review is organized in sections including life cycle and risk assessments; characteristics, quality, and measurement including micropollutants, nanoparticles, pathogens, and metals; sludge treatment technologies including dewatering, digestion, composting, and wetlands; disposal and reuse including adsorbents, land application and agricultural uses, nutrient recovery, and innovative uses; odor and air emissions; and energy issues.

Hydrothermal Carbonization as a Strategy for Sewage Sludge Management: Influence of Process Withdrawal Point on Hydrochar Properties

Conventional activated sludge systems, still widely used to treat wastewater, produce large amounts of solid waste that is commonly landfilled or incinerated. This study addresses the potential use of Hydrothermal Carbonization (HTC) to valorize sewage sludge residues examining the properties of hydrochars depending on HTC process conditions and sewage sludge withdrawal point. With increasing HTC severity (process residence time and temperature), solid yield, total Chemical Oxygen Demand (COD) and solid pH decrease while ash content increases. Hydrochars produced from primary (thickened) and secondary (digested and dewatered) sludge show peculiar distinct properties. Hydrochars produced from thickened sludge show good fuel properties in terms of Higher Heating Value (HHV) and reduced ash content. However, relatively high volatile matter and O:C and H:C ratios result in thermal reactivity significantly higher than typical coals. Both series of carbonized secondary sludges show neutral pH, low COD, enhanced phosphorous content and low heavy metals concentration: as a whole, they show properties compatible with their use as soil amendments.

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

This study aims to investigate the sewage sludge (SS) drying process by incorporating a by-product formed in the pulp and paper industry (green liquor dregs - GLD) as drying adjuvant. Through an innovative approach, the drying kinetics was modelled, and the final dried product was tested for soil applications. After the characterization phase, small cylinders of SS without and with 0.15 g GLD g SS^-1_wb (SS_GLD) were dried in isothermal conditions at 70, 100, and 130 °C. The experimental data were fitted by Fick's second law and thin-layer models, and good results were achieved in both cases (R² > 0.98 and RMSE <0.05). Although only a slight improvement was observed, the best conditions for drying biosolids were found with the addition of GLD at 130 °C, where the drying rate was 30.88 gH₂O kg^-1 SS_wb min^-1. In this condition, a decrease of 8% in the energy required for moisture evaporation was observed. Regarding the phytotoxicity tests with Lepidium sativum L. (garden cress), 60% improvement in EC₅₀ was noticed for the sample with GLD when compared to the raw SS. The dried product SS_GLD complied with the regulations for soil applications regarding the potentially toxic metals (Cr, Ni, Cu, Pb, Zn, and Cd), and promoted an increase in soil organic matter and pH. However, further and in-depth studies should be conducted to assess the potential of SS_GLD application in agricultural soil.

Migration characteristics and toxicity evaluation of heavy metals during the preparation of lightweight aggregate from sewage sludge

A lightweight aggregate (LWA) was manufactured from municipal sewage sludge, gangue, and coal ash. The product performance and environmental safety of the sintered material were evaluated by changing the sludge blending ratio and sintering temperature. The distribution and migratory transformation characteristics of heavy metals in LWA were examined by BCR sequential extraction in combination with inductively coupled plasma optical emission spectrometry (ICP-OES). The environmental safety performance of LWA was comprehensively evaluated by the OPTI index for the first time. The leaching concentration of the heavy metals Pb, Ni, Cu, and Zn in raw materials without sintering reached 1.17, 1.6, 7.84, and 7.56 mg/L, respectively, far exceeding the regulatory threshold value. At 1250 °C, sintering with 60% sludge content resulted in Cu and Zn leaching concentrations of only 0.41 mg/L and 0.37 mg/L, respectively. Furthermore, a big portion of heavy metals were in the residual fraction of sintered LWA. The proportion of comprehensive pollutant toxicity index is only 199.17. Additionally, the mechanical properties of sintered LWA exceed the standards stipulated in the GB/T1743.1-2010 standard. Using sewage sludge to manufacture lightweight aggregate is not only environmentally safe but also produces LWA with good engineering characteristics.