Toxicity and physicochemical parameters of composts including distinct residues from agribusiness and slaughterhouse sludge

Reuse of lime sludge from immediate one-step lime precipitation process as a coagulant (aid) in slaughterhouse wastewater treatment

The circularity of wastewater treatment subproducts is on the worldwide agenda. In this way, this work aims to evaluate alternatives for the reuse of sludge from slaughterhouse wastewater treatment. Wetted sludges produced in the immediate one-step lime precipitation process were applied directly or first calcined, as a coagulant or coagulant aid, in the absence or presence of Ca(OH)₂, to slaughterhouse wastewaters with different characteristics. For the best sludge reuse, successive reuses of the sludge were carried out and the characteristics of treated slaughterhouse wastewater were evaluated after each reuse. Results showed a great similarity between slaughterhouse and treated slaughterhouse wastewaters using wetted and calcined sludges as a coagulant for highly contaminated slaughterhouse wastewater. In addition, a great similarity was also observed between the calcined and the wetted sludges, both as a coagulant aid, for all the slaughterhouse wastewaters tested. However, the latter consumed more hydrated lime, more volume of sludge sedimented, and higher concentrations phosphorus and organic matter in the treated wastewater. Calcined sludge as a coagulant aid guaranteed the best slaughterhouse wastewater quality for almost of the tested paramenters (≥94% for absorbances at 254 nm and 410 nm, E. coli, turbidity, and phosphorus, chemical oxygen demand between 3 and 91%, and total Kjeldahl nitrogen between 3 and 62%) independently of the wastewater characteristics. Calcined sludge as a coagulant aid can be three times reused for the tested parameters and slaughterhouse wastewater characteristics without significantly decreasing the quality. The successive sludge reused saves the hydrated lime dose applied (up to 28.4%) and the sedimented sludge volume (up to 24.7%), and can be a solution to stabilize sludge due to the pH increase (sludge pH = 12).

Optimization of composting methods for efficient use of cassava waste, using microbial degradation

With the recent revolution in the green economy, agricultural solid waste resource utilization has become an important project. A small-scale laboratory orthogonal experiment was set up to investigate the effects of C/N ratio, initial moisture content and fill ratio (v_{cassava residue}: v_gravel) on the maturity of cassava residue compost by adding Bacillus subtilis and Azotobacter chroococcum. The highest temperature in the thermophilic phase of the low C/N ratio treatment is significantly lower than the medium and high C/N ratios. The C/N ratio and moisture content have a significant impact on the results of cassava residue composting, while the filling ratio only has a significant impact on the pH value and phosphorus content. Based on comprehensive analysis, the recommended process parameters for pure cassava residue composting are a C/N ratio of 25, an initial moisture content of 60%, and a filling ratio of 5. Under these conditions, the high-temperature conditions can be reached and maintained quickly, the organic matter has been degraded by 36.1%, the pH value has dropped to 7.36, the E4/E6 ratio is 1.61, the conductivity value has dropped to 2.52 mS/cm, and the final germination index increased to 88%. The thermogravimetry, scanning electron microscope, and energy spectrum analysis also showed that the cassava residue was effectively biodegraded. Cassava residue composting with this process parameter has great reference significance for the actual production and application of agriculture.

Moisture content monitoring in industrial-scale composting systems using low-cost sensor-based machine learning techniques

Moisture is a key aspect for proper composting, allowing greater efficiency and lower environmental impact. Low-cost real-time moisture determination methods are still a challenge in industrial composting processes. The aim of this study was to design a model of hardware and software that would allow self-adjustment of a low-cost capacitive moisture sensor. Samples of organic composts with distinct waste composition and from different composting stages were used. Machine learning techniques were applied for self-adjustment of the sensor. To validate the model, results obtained in a laboratory by the gravimetric method were used. The proposed model proved to be efficient and reliable in measuring moisture in compost, reaching a correlation coefficient of 0.9939 between the moisture content verified by gravimetric analysis and the prediction obtained by the Sensor Node.

Continuously applying compost for three years alleviated soil acidity and heavy metal bioavailability in a soil-asparagus lettuce system

Soil acidification and heavy metal pollution are two common barrier factors threatening plant growth and agro-product quality. Applying manure compost is promising to alleviate soil acidity, while it may increase heavy metal accumulation in soil. In a 3-year field experiment, compost was applied for 12 consecutive harvest seasons at 15, 30, and 45 t ha^-1 in a slightly acidic soil. Samples were taken at the twelfth season to examine the changes of soil properties, vegetable productivity, heavy metal accumulation and bioavailability in the soil-asparagus lettuce system. The results showed that the pH values of the topsoil were increased by 0.49-0.75 units in compost added soils compared with no compost control, soil organic matter (SOM) contents and cation exchange capacity (CEC) were increased by 34-101% and 43-44%, respectively. The soil nutrient contents were also increased in compost treatments. Continuously applying compost increased Cd, Cu, and Zn concentrations in topsoil by up to 32, 20, and 22% and decreased Pb by 10%, while soil available Cd and Zn concentrations were reduced by up to 54 and 86%, and available Cu was increased by 19-63%. The biomass of asparagus lettuce was increased by 30-59% in compost treatments, with Cd and Zn concentrations in the plant tissues reduced by 28-50% and 14-67%. Cu concentrations in the lettuce shoots were increased by 20-39%. The concentration factor and total uptake of Cd and Zn in lettuce were effectively reduced in compost treatments. Cd was more prone to be taken up, translocated and accumulated from soil to the lettuce plant than the other heavy metals. Continuously applying compost over 3 years increased soil pH, SOM, CEC, nutrient contents, and lettuce productivity, decreased Cd and Zn bioavailability in the soil-lettuce system, while posing a risk of increasing heavy metal accumulation in topsoil.

Role of composted tannery solid waste and its autochthonous microbes in enhancing phytoextraction of toxic metals and stress abatement in sunflower

The excessive concentration of multiple heavy metals in the tannery solid waste (TSW) needs integrated process solutions for its decontamination. This study is aimed at deriving TSW compost and autochthonous microbe synergies for improving phytoextraction potential of sunflower. In-vessel composting of TSW was carried out by using fruit waste as an inoculum to achieve the optimized conditions. Autochthonous strains of Trichoderma viride and Bacilllus sp. isolated from TSW were utilized individually as well as in combination with TSWC amendments of 2.5, 5 and 10% (w/w) prepared in our pilot scale experiment. Analyses of TSW compost based on FTIR and SEM illustrated the wide range of functionality and porosity along the mesh of fungal hyphae and inorganic moieties present on the compost surface. Plant biomass and TMs uptake (Cr 540 mg kg^-1 > Cd 330 mg kg^-1 > Pb 285 mg kg^-1) were significantly pronounced in shoots of sunflower under combined treatments at 10% TSWC amended soils. However, in seeds, TMs were found below detection limit (BDL) through atomic absorption spectrophotometry. Biochemical assays of sunflower including total chlorophyll content (18%), total soluble protein (45%), superoxide dismutase (80%) and catalase (75%) activities were also increased significantly at higher level of amendment in combination with microbes than in the control. Despite being high in TMs, high biomass in sunflower and associated elevation in biochemical products demonstrate the potential of TSW for valorization.Novelty statement: This study identifies the cost-effective management of multi metal contaminated tannery solid waste through deriving its compost along with autochthonous microbes as phytoextraction assistants by yielding higher plant biomass. This study suggests the use of composted TSW inoculated with selected autochthonous fungi and bacteria for enhancing sunflower's biomass and enhancing the bioavailable fractions of toxic metals for phytoextraction.