Construction, renovation and demolition (CRD) wastes contaminated by gypsum residues: Characterization, treatment and valorization.

Management of wastes resulting from construction, renovation and demolition (CRD) activities has become an important challenge for scientists. The recovery of gypsum residues from CRD waste is one of the solutions to minimize the impact of CRD operations on the environment. This review discusses the characteristics of CRD waste, different treatment and valorization methods for both CRD waste and extracted gypsum residues. Pre-treatment based on particle size separation is the most fundamental step in the process of extracting gypsum residues from CRD fine tailings. The subsequent application of a physical, chemical or biological decontamination approach on the gypsum residues could significantly improve its quality as compared to natural gypsum. The quality of the gypsum obtained affects its valorization potential in different sectors such as cement manufacturing, the sequestration of carbon dioxide and nutrients. The valorization strategy could help reducing emissions of greenhouse gases while producing by-products that can be reused in agriculture. As such, this review may provide guidance for more sustainable management of CRD and gypsum residues in the future.

Passive phosphorus capture in biofiltration context: nitrate impact on the performance.

Research on the development of a passive phosphorus entrapment process characterized by biofilters with active wood-based media impregnated with iron hydroxide has been conducted. Phosphorus removal was done by sorption which includes adsorption, exchange of ions and precipitation. Experiments were performed in order to investigate the effect of nitrate, generally present at the end of secondary treatment, on the phosphorus removal performance. Columns tests were performed with anaerobic activated wood-based media and immersion over a period of 150 days. Columns were fed for 32 days with a synthetic solution of 5 mg P L-1. Different concentrations of nitrate (5, 10 and 25 mg N-NO3 L-1) were then applied on three columns (C2, C3 and C4), column C1 serving as a control. Results showed total phosphorus (TP) removal efficiencies of 96.9%, 81.7%, 70.6% and 75.7%, respectively, for C1, C2, C3 and C4. Addition of nitrate increases the oxidoreduction potential (ORP). This results in an inhibition of the reductive dissolution, characterized by a decrease in the release of ferrous ions. Simultaneous denitrification occurs within the columns. It is both biological and chemical through the oxidation of ferrous ions by NO2, produced during biological denitrification. Furthermore, bacterial identification tests have highlighted the presence of iron-related bacteria (Pseudomonas, Thiobacillus, Enteric bacteria, e.g. E. coli), slym forming bacteria, sulphate reducing bacteria and denitrifying microorganisms such as Pseudomonas and E. bacteria in biofilters.

Hydrolytic pre-treatment methods for enhanced biobutanol production from agro-industrial wastes.

Brewery industry liquid waste (BLW), brewery spent grain (BSG), apple pomace solid wastes (APS), apple pomace ultrafiltration sludge (APUS) and starch industry wastewater (SIW) have been considered as substrates to produce biobutanol. Efficiency of hydrolysis techniques tested to produce fermentable sugars depended on nature of agro-industrial wastes and process conditions. Acid-catalysed hydrolysis of BLW and BSG gave a total reducing sugar yield of 0.433 g/g and 0.468 g/g respectively. Reducing sugar yield from microwave assisted hydrothermal method was 0.404 g/g from APS and 0.631 g/g from APUS, and, 0.359 g/g from microwave assisted acid-catalysed SIW dry mass. Parameter optimization (time, pH and substrate concentration) for acid-catalysed BLW hydrolysate utilization using central composite model technique produced 307.9 g/kg glucose with generation of inhibitors (5-hydroxymethyl furfural (20 g/kg), furfural (1.6 g/kg), levulinic acid (9.3 g/kg) and total phenolic compound (0.567 g/kg)). 10.62 g/L of acetone-butanol-ethanol was produced by subsequent clostridial fermentation of the substrate.

Potential Application of Biohydrogen Production Liquid Waste as Phosphate Solubilizing Agent-A Study Using Soybean Plants.

With CO2 free emission and a gravimetric energy density higher than gasoline, diesel, biodiesel, and bioethanol, biohydrogen is a promising green renewable energy carrier. During fermentative hydrogen production, 60-70 % of the feedstock is converted to different by-products, dominated by organic acids. In the present investigation, a simple approach for value addition of hydrogen production liquid waste (HPLW) containing these compounds has been demonstrated. In soil, organic acids produced by phosphate solubilizing bacteria chelate the cations of insoluble inorganic phosphates (e.g., Ca3 (PO4)2) and make the phosphorus available to the plants. Organic acid-rich HPLW, therefore, has been evaluated as soil phosphate solubilizer. Application of HPLW as soil phosphate solubilizer was found to improve the phosphorus uptake of soybean plants by 2.18- to 2.74-folds. Additionally, 33-100 % increase in seed germination rate was also observed. Therefore, HPLW has the potential to be an alternative for phosphate solubilizing biofertilizers available in the market. Moreover, the strategy can be useful for phytoremediation of phosphorus-rich soil.