Behavior of Heavy Metals during the Agro-Industrial Wastes Gasification

The characterization analysis of three agro-industrial wastes was performed in order to study its thermal gasification. Some analyses such as determination of Ca, K and Mg concentration and determination of three representative toxic metals concentration Cd, Cr and Pb in all its oxidation states and the fundamental state, were carried out. The heavy metals concentration was also determined in the ashes obtained during the gasification process. The mobility of these elements was studied through three leaching tests. The behavior of heavy metals, sulfur and chlorine compounds, was predicted considering the presence of water vapor, syngas, Ca, Mg, K, Si, Al and other ash components. The heavy metals are not more concentrated in the gasification ash;these pollutants are released during this process. Ca, Mg and K presence in these residues would promote the pollutants retention. The ash of the studied waste can be disposed in controlled landfills or used in road construction, according to the obtained results during the leaching test DIN-DEV S4. The obtained results in the leaching test EPA 1311 TLCP classify these gasification ashes as no toxic waste.

Biotechnological potential of agro-industrial wastes for protein enrichment by solid-state fermentation using Aspergillus niger

This study is to assess the biotechnological potential of agro-industrial wastes of pineapple(Ananas comosus),sweet potato(Ipomoea batatas)and watermelon(Citrullus lanatus)for protein enrichment by solid-state fermentation using Aspergillus niger.Spore suspensions of A.niger were prepared with potato dextrose broth that had been supplemented with sodium chloride,ammonium nitrate and thiamine,and adjusted to pH of 5.Initial protein contents of sterile and non-sterile wastes of the pineapple,sweet potato,and watermelon were determined by the Kjeldahl method.The remaining sterile and non-sterile wastes was inoculated with spore suspensions of A.niger and incubated at temperature of 24℃ under conditions of solid-state fermentation for 14 days.Protein contents of the inoculated sterile and non-sterile wastes were determined after 7 and 14 days.The sterile wastes of pineapple,sweet potato and watermelon recorded initial percentage protein contents of 4.37,4.39,and 10.89,respectively,whereas their corresponding non-sterile wastes recorded initial percentage protein contents of 3.76,4.00,and 10.16,respectively.The results further show that percentage increase in protein content of sterile wastes after 14 days of fermentation were pineapple,35.01%;sweet potato,27.60%;and watermelon,64.40%.Percentage increase in protein content of non-sterile wastes after 14 days of fermentation were pineapple,72.34%;sweet potato,85.25%;and watermelon,80.51%.These findings affirm the biotechnological potential of pineapple,sweet potato and watermelon wastes and the importance of fungi as agents for protein enrichment of agro-industrial wastes.

Optimizing Household Wastes (Rice, Vegetables, and Fruit) as an Environmentally Friendly Electricity Generator

The high consumption of electricity and issues related to fossil energy have triggered an increase in energy prices and the scarcity of fossil resources.Consequently,many researchers are seeking alternative energy sources.One potential technology,the Microbial Fuel Cell(MFC)based on rice,vegetable,and fruit wastes,can convert chemical energy into electrical energy.This study aims to determine the potency of rice,vegetable,and fruit waste assisted by Cu/Mg electrodes as a generator of electricity.The method used was a laboratory experiment,including the following steps:electrode preparation,waste sample preparation,incubation of the waste samples,construction of a reactor using rice,vegetable,and fruit waste as a source of electricity,and testing.The tests included measuring electrical conductivity,electric current,voltage,current density,and power density.Based on the test results,the maximum current and voltage values for the fruit waste samples were 5.53 V and 11.5 mA,respectively,with a current density of 2.300 mA/cm^(2) and a power density of 12.719 mW/cm^(2).The results indicate the potential for a future development.The next step in development involves determining the optimum conditions for utilizing of rice,vegetable,and fruit waste.The results of the electrical conductivity test on rice,vegetable,and fruit waste samples were 1.51,2.88,and 3.98 mS,respectively,with the highest electrical conductivity value found in the fruit waste sample.

Bird’s-eye view of recycled solid wastes in road engineering

Recent trends in road engineering have explored the potential of incorporating recycled solid wastes into infrastructures that including pavements,bridges,tunnels,and accessory structures.The utilization of solid wastes is expected to offer sustainable solutions to waste recycling while enhancing the performance of roads.This review provides an extensive analysis of the recycling of three main types of solid wastes for road engineering purposes:industrial solid waste,infrastructure solid waste,and municipal life solid waste.Industrial solid wastes suitable for road engineering generally include coal gangue,fly ash,blast furnace slag,silica fume,and steel slag,etc.Infrastructure solid wastes recycled in road engineering primarily consist of construction&demolition waste,reclaimed asphalt pavements,and recycled cement concrete.Furthermore,recent exploration has extended to the utilization of municipal life solid wastes,such as incinerated bottom ash,glass waste,electronics waste,plastic waste,and rubber waste in road engineering applications.These recycled solid wastes are categorized into solid waste aggregates,solid waste cements,and solid waste fillers,each playing distinct roles in road infrastructure.Roles of solid waste acting aggregates,cements,and fillers in road infrastructures were fully investigated,including their pozzolanic properties,integration effects to virgin materials,modification or enhancement solutions,engineering performances.Utilization of these materials not only addresses the challenge of waste management but also offers environmental benefits aiming carbon neutral and contributes to sustainable infrastructure development.However,challenges such as variability in material properties,environmental impact mitigation,secondary pollution to environment by leaching,and concerns regarding long-term performance need to be further addressed.Despite these challenges,the recycled solid wastes hold immense potential in revolutionizing road construction practices and fostering environmental stewardship.This review delves into a bird’seye view of the utilization of recycled solid wastes in road engineering,highlighting advances,benefits,challenges,and future prospects.

CO_(2) mineralization by typical industrial solid wastes for preparing ultrafine CaCO_(3): A review

Mineral carbonation is a promising CO_(2) sequestration strategy that can utilize industrial wastes to convert CO_(2) into high-value CaCO_(3).This review summarizes the advancements in CO_(2) mineralization using typical industrial wastes to prepare ultrafine CaCO_(3).This work surveys the mechanisms of CO_(2) mineralization using these wastes and its capacities to synthesize CaCO_(3),evaluates the effects of carbonation pathways and operating parameters on the preparation of CaCO_(3),analyzes the current industrial application status and economics of this technology.Due to the large amount of impurities in solid wastes,the purity of CaCO_(3) prepared by indirect methods is greater than that prepared by direct methods.Crystalline CaCO_(3) includes three polymorphs.The polymorph of CaCO_(3) synthesized by carbonation process is determined the combined effects of various factors.These parameters essentially impact the nucleation and growth of CaCO_(3) by altering the CO_(2) supersaturation in the reaction system and the surface energy of CaCO_(3) grains.Increasing the initial pH of the solution and the CO_(2)flow rate favors the formation of vaterite,but calcite is formed under excessively high pH.Vaterite formation is favored at lower temperatures and residence time.With increased temperature and prolonged residence time,it passes through aragonite metastable phase and eventually transforms into calcite.Moreover,polymorph modifiers can decrease the surface energy of CaCO_(3) grains,facilitating the synthesis of vaterite.However,the large-scale application of this technology still faces many problems,including high costs,high energy consumption,low calcium leaching rate,low carbonation efficiency,and low product yield.Therefore,it is necessary to investigate ways to accelerate carbonation,optimize operating parameters,develop cost-effective agents,and understand the kinetics of CaCO_(3) nucleation and crystallization to obtain products with specific crystal forms.Furthermore,more studies on life cycle assessment(LCA)should be conducted to fully confirm the feasibility of the developed technologies.

Biochemical, functional and antioxidant potential of higher fungi cultivated on agro-industrial residues. Part Ⅱ: Cultures on mixtures of spent mushroom substrates and mushroom cropping by-products

Novel substrates consisted of different fresh agro-industrial residues,their corresponding and commercial spent mushroom substrates(i.e.SMS deriving from laboratory-scale experiments and SMS deriving from industrial-scale experiments by Green Zin S.A.-SMS GZ)and Pleurotus waste(PW;stipes/mishappen mushrooms)were used in blends for a new cultivation cycle of Pleurotus ostreatus and P.eryngii mushrooms in bags.Their impact on the biochemical properties(intra-cellular polysaccharides-IPSs,protein,lipid,total phenolic compounds-TPCs,individual carbohydrates composition of the IPSs)in the first-and second-flush whole mushrooms,pilei and stipes,as well as the fatty acids composition,the antioxidant activity(in the first-flush mushroom parts)and glucan content of stipes were examined.Both species produced satisfactory IPSs quantities in all substrates(28.69-46.38%,w/w)and significant protein amounts(18.37-26.80%,w/w).The further SMS addition(80%,w/w instead of 40%,w/w)in the cultivation substrates affected positively the mushroom IPSs values,whereas the highest protein content was detected in mushroom’s parts cultivated on substrates consisted of fresh agro-industrial residues.Mushroom’s lipid content was affected differently by the various substrate combinations,with SMS presence resulting in mushrooms with a lower fat content than those produced in substrates with PW addition.Fresh substrates with PW and those with coffee residue were the most favorable for TPCs production.Regarding production flushes,the nutritional value of mushrooms was comparable between them,only a slight increase in TPCs of second-flush carposomes was detected.Glucose was the predominant monosaccharide of the produced IPSs,combined with a significant production of total and β-glucans.SMSs and PW addition had a positive impact on antioxidant activity,too.A higher quantity of lipids,TPCs and significant antioxidant activity were detected in all Pleurotus pilei than stipes,whereas the latter were richer in IPSs.Both pilei and stipes had a significant protein amount.Hence,the data obtained by this study support the positive effect of different types of SMS and mushroom waste on P.ostreatus and P.eryngii nutritional value.

Agro-Industrial Waste Materials as Substrates for the Production of Poly(3-Hydroxybutyric Acid)

Accumulation of recalcitrant plastics in the environment has become a world-wide problem in today’s societies. Rapid depletion of natural resources for synthetic plastics along with environmental concerns has directed research towards finding alternatives to petroleum-based polymers. Poly(3-hydroxybutyric acid) P(3HB), as one of these alternatives, have attracted much attention in recent years due to their varied mechanical properties, biocompatibility and biodegradability. The aim of this study was to identify an agro-industrial waste resource economically suitable for large-scale production of P(3HB), to optimize the production using Response Surface Methodology in small-scale and subsequently, to test the production in a continuously stirred tank reactor. Among a range of agro-industrial waste, orange peel was selected as the most suitable for P(3HB) production. P(3HB) concentration of 1.24 g P(3HB)/L culture broth with 41% P(3HB)/dcw yield was obtained using orange peel as the sole carbon source in optimized medium with a modified strain of Bacillus subtilis (B. subtilis OK2).

Utilization of Agro-Industrial Residues and Municipal Waste of Plant Origin for Cellulosic Ethanol Production

Today’s search for alternative sources of energy to reduce the use of fossil fuels is motivated by environmental, socioeconomic and political reasons. The use of agro-industrial and municipal wastes of plant origin for ethanol production appears to be the best option to solve the dilemma of using food sources to produce biofuels, since it adds value to these wastes in eco-efficient processes. This paper highlights the potential of agro-industrial and municipal wastes for cellulosic ethanol production.

Study of the Production of Lentinus crinitus(L.)Fr.Lignolytic Enzymes Grown on Agro-Industrial Waste

Exclusively Brazilian, the Caatinga biome has been thus far a place of very few studies on the Basidiomycetes fungi. Due to its semiarid climate, fungi found in the region are likely to carry lignolytic enzymes which hold biotechnological potential to be used in industrial processes of agro-industrial residue bioconversion. This study performed a response surface statistical planning to optimize the secretion of enzymes such as laccase (Lac), lignin peroxidase (LiP) and manganese peroxidase (MnP) by Lentinus crinitus. Three variables were under analysis: different concentrations of barley and cassava residue, pH and temperature. MnP enzyme showed the highest enzymatic activity rate (23.5 IU/L). Additionally, MnP had the best results of enzyme secretion for substrate composition of 50% barley and 50% cassava, at pH 7 and temperature at 28°C for a 28-day incubation period. However, further studies are pivotal to test the efficiency in lignin bioconversion by the enzymes synthesized in this work and also to establish their usage pattern on a large scale.

Soil properties in reclaimed farmland by filling subsidence basin due to underground coal mining with mineral wastes in China

Reclaimed mining-induced subsidence area soils (RMSs) could restore soil quality and crop productivity in coal mining area. This study was conducted to evaluate the effects of mineral-processing wastes (fly ash vs coal gangue) as backfill substrates on soil chemical and microbial properties in mining-induced subsidence area. A general higher water holding capacity (WHC) and pH had been observed in fly ash than coal gangue reconstructed soil. Soil microbial biomass C (MBC) and N (MBN), MBC/TOC (total organic carbon) ratio (qmic) were higher under the influence of the fly ash, while contents of As, Cr, C/Nbio, the basal respiration per unit of microbial biomass (QCO2) were higher under the coal gangue reconstructed mode in 0-10, 10-20, 20-50 cm layers. The microbial basal respiration was higher in 0-10, 10-20, 0-50 cm layers, while was lower in 20-50 cm layer under fly ash than that of coal gangue reconstructed mode. The lower QCO2 of fly ash mine soil suggested the lower maintenance energy requirement of the microbial community. Moreover, the contents of metals may possibly have negative implications for soil microbial and enzyme activities in reconstructed soil.

Adsorption characteristics of Pb from urban stormwater runoff by construction wastes

Construction wastes were selected as the adsorbents and static and dynamic adsorption batch experiments were carried out to investigate the adsorption of Pb to construction wastes with different particle size gradations in the simulated stormwater runoff system.The experimental results show that the pseudo-second-order kinetics model can better characterize the adsorption process of Pb than the pseudo-first-order kinetics model.The adsorption equilibrium data can be well fitted by the Freundlich isotherm model. The construction wastes with different tested size gradations can greatly remove Pb from stormwater runoff and their average removal rate can reach up to 99%.The construction wastes with narrow size distribution can better remove Pb but with worse permeability than those with wide size distribution. The particle size gradation of construction wastes greatly influences the equilibrium time rate and the capacity of Pb adsorption.The equilibrium adsorption rate and capacity are 18.1 μg/min and 5.5 μg/g respectively for the construction wastes with the size of 2.36 to 4.75 mm which are the greatest among the different size gradations.The present study provides a scientific basis for effectively controlling Pb pollution from stormwater runoff and the construction wastes resource utilization.

Environmental risk assessment on slag and iron-rich matte produced from reducing-matting smelting of lead-bearing wastes and iron-rich wastes

A new process for utilization of hazardous lead-bearing wastes and iron-rich wastes by reducing-matting smelting has been developed.The slag（SG） and the iron-rich matte（IRM） are the main by-products from reducing-matting smelting of lead-bearing wastes and iron-rich wastes.The environmental risk of heavy metals（Cd,Zn,Pb and As） in the main by-products versus the charging material for reducing-matting smelting（CM） has been systematically assessed using leaching toxicity test,the three-stage sequential extraction procedure of European Community Bureau of Reference（BCR） and Hakanson Potential Ecological Risk Index Method（PERI）.The results demonstrate that the ecological risk level of heavy metals for SG and IRM is significantly reduced after the reducing-matting smelting process compared with that for CM.

Problems of Identification according to National Catalogue of Hazardous Wastes

ldentification work of solid wastes ’ risks is a kind of improvement and amendment for environmental impact assessment document of constructed projectss. ln the research, waste identification is classified as per entrustment source and the characteristics of pol ution accidents are analyzed, with major problems of National Catalogue of Hazardous Wastes and countermeasures proposed.

Research Advances in Agricultural Reutilization of Urban-rural Organic Wastes

The author summarized the advantages and potential risks of urban-rural organic wastes agricultural reutilization to reduce the potential risks of urban-rural organic wastes agricultural utilization. The results showed that： the organic wastes generated in urban-rural life as fertilizer applied into farmland made an impact on soil properties, then indirectly affected the soil microbial biomass and soil enzymes activities. In addition, the heavy metals in organic wastes would accumulate in the soil and damage to soil environment. Therefore, it was necessary to make a long- term research on the environment of soil which agricultural utilized of wastes.

Start-up performances of dry anaerobic mesophilic and thermophilic digestions of organic solid wastes

Two dry anaerobic digestions of organic solid wastes were conducted for 6 weeks in a lab-scale batch experiment for investigating the start-up performances under mesophilic and thermophilic conditions. The enzymatic activities, i.e., β-glucosidase, N-α-benzoyl-Largininamide （BAA）-hydrolysing protease, urease and phosphatase activities were analysed. The BAA-hydrolysing protease activity during the first 2-3 weeks was low with low pH, but was enhanced later with the pH increase. β-Glucosidase activity showed the lowest values in weeks 1-2, and recovered with the increase of BAA-hydrolysing protease activity. Acetic acid dominated most of the total VFAs in thermophilic digestion, while propionate and butyrate dominated in mesophilic digestion. Thermophilic digestion was confirmed more feasible for achieving better performance against misbalance, especially during the start-up period in a dry anaerobic digestion process.

Influence of lactic acid on the two-phase anaerobic digestion of kitchen wastes

To evaluate the influence of lactic acid on the methanogenesis, anaerobic digestion of kitchen wastes was firstly conducted in a two-phase anaerobic digestion process, and performance of two digesters fed with lactic acid and glucose was subsequently compared. The results showed that the lactic acid was the main fermentation products of hydrolysis-acidification stage in the two-phase anaerobic digestion process for kitchen wastes. The lactic acid concentration constituted approximately 50% of the chemical oxygen demand （COD） concentration in the hydrolysis-acidification liquid. The maximum organic loading rate was lower in the digester fed with lactic acid than that fed with glucose. Volatile fatty acids （VFAs） and COD removal were deteriorated in the methanogenic reactor fed with lactic acid compared to that fed with glucose. The specific methanogenic activity （SMA） declined to 0.343 g COD/（gVSS-d） when the COD loading were designated as 18.8 g/（L-d） in the digester fed with lactic acid. The propionic acid accumulation occurred due to the high concentration of lactic acid fed. It could be concluded that avoiding the presence of the lactic acid is necessary in the hydrolysis-acidification process for the improvement of the two-phase anaerobic digestion process of kitchen wastes.

Preparation and characterization of high-strength calcium silicate boards from coal-fired industrial solid wastes

To realize the comprehensive utilization of coal-fired industrial solid wastes, a novel high-strength board was prepared from calcium silicate slag, fly ash, and flue gas desulfurization(FGD) gypsum. The changes in mineral phases, chemical structure, and morphology during hydration were investigated by X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), and scanning electron microscopy(SEM). A traditional board made from quartz and lime was prepared as a reference. The novel board not only consumes a lot of solid wastes, but also meets the strength requirement of the class-five calcium silicate board according to the Chinese Standard JC/T 564.2—2008. Microanalysis showed that hydrated calcium silicate gel(C-S-H(I)), ettringite, tobermorite, and xonotlite were successively generated in the novel board by synergistic hydration of the mixed solid wastes. The board strength was improved by the formation of tobermorite and xonotlite but decreased by unhydrated quartz. It was demonstrated that quartz was not completely hydrated in the traditional board. As a result, the flexural strength of the traditional board was much lower than that of the novel board.

Laboratory scale studies on removal of chromium from industrial wastes

Chromium being one of the major toxic pollutants is discharged from electroplating and chrome tanning processes and is also found in the effluents of dyes, paint pigments, manufacturing units etc. Chromium exists in aqueous systems in both trivalent (Cr 3+) and hexavalent (Cr 6+) forms. The hexavalent form is carcinogenic and toxic to aquatic life, whereas Cr 3+ is however comparatively less toxic. This study was undertaken to investigate the total chromium removal from industrial effluents by chemical means in order to achieve the Pakistan NEQS level of 1 mg/L by the methods of reduction and precipitation. The study was conducted in four phases. In phase Ⅰ, the optimum pH and cost effective reducing agent among the four popular commercial chemicals was selected. As a result, pH of 2 was found to be most suitable and sodium meta bisulfate was found to be the most cost effective reducing agent respectively. Phase Ⅱ showed that lower dose of sodium meta bisulfate was sufficient to obtain 100 % efficiency in reducing Cr 6+ to Cr 3+, and it was noted that reaction time had no significance in the whole process. A design curve for reduction process was established which can act as a tool for treatment of industrial effluents. Phase Ⅲ studies indicated the best pH was 8.5 for precipitation of Cr 3+ to chromium hydroxide by using lime. An efficiency of 100 % was achievable and a settling time of 30 minutes produced clear effluent. Finally in Phase Ⅳ actual waste samples from chrome tanning and electroplating industries, when precipitated at pH of 12 gave 100 % efficiency at a settling time of 30 minutes and confirmed that chemical means of reduction and precipitation is a feasible and viable solution for treating chromium wastes from industries.

Formation cause,composition analysis and comprehensive utilization of rare earth solid wastes

Based on practical situation of rare earth industrial chain,production process and rare earth materials that could produce solid wastes on batch were discussed.Formation cause,formation volume,composition analysis and comprehensive utilization of the solid wastes of rare earth hydrometallurgy slag,electrolysis slag,Fe-based rare earth permanent magnetic materials,Co-based rare earth permanent magnetic materials,rare earth hydrogen storage materials,rare earth polishing powders and rare earth catalysts were ...

Co-inhibition of methanogens for methane mitigation in biodegradable wastes

The inhibition effects and mechanisms of chlorinated methane and acetylene on methanogenesis in the anaerobic digestion process of the biodegradable wastes were investigated.It was found that both chloroform and acetylene could effectively inhibit methanogens while the biodegradability of the wastes was not affected.Acetylene inhibited the activity of methanogens,while chloroform inhibited metabolic process of methanogenesis.A central composite design（CCD） and response surface regression analysis（RSREG） were employed to determine the optimum conditions and interaction effects of chloroform and acetylene in terms of inhibition effciency,production of volatile fatty acids（VAF） and molar ratio of propionic acid to acetic acid.Chloroform had significant effect on enhancing the production of VFA（F = 121.3;p 〈 0.01）,and acetylene promoted the inhibition effciency（F = 99.15;p 〈 0.05） more effectively than chloroform（F = 9.72;p 〉 0.05）.In addition,a maximum molar ratio of propionic acid to acetic acid of 1.208 was estimated under the optimum conditions of chloroform concentration of 9.05 mg/kg and acetylene concentration of 3.6×10^-3（V/V）.Hence,methanogens in the wastes can be inhibited while the stabilization process of the biodegradable wastes can still work well,as propionic acid generated during the inhibition process could hardly be utilized by methanogens.