Digestibility Improvement of Sorted Waste with Alkaline Hydrothermal Pretreatment

The digestibility of sorted municipal solid waste （MSW） is often limited by the high content of structured green waste. The objectives of this study are to investigate the effect of alkaline hydrothermal pretreatment on the anaerobic digestion of sorted waste and to analyze the biogas production of different parts of the waste. The waste was hydrothermally pretreated in a dilute alkali solution. The hydrolysis product was then incubated in a 500 mL saline bottle to determine the biochemical methane potential （BMP） under mesophilic anaerobic conditions. The optimum hydrothermal condition was 170℃ at 4 g NaOH/100 g solid for one hour. The concentration of chemical oxygen demand （COD） was 13 936 mg/L and the methane yield was 164 mL/g volatile solid （VS） for 6 days incubation at the optimum conditions. The biogas production was increased more than 50% over the control, with the methane conversion ratio on a carbon basis enhanced to 30.6%. The organic part of the sorted waste was mainly kitchen garbage and leaves. Model kitchen garbage completely liquified at 130℃ for one hour had a methane yield of 276 mL/g VS. The alkali addition slightly enhanced the hydrolyzation rate and methane yield. The biogas potential of leaves was improved by pretreatment at above 150℃ under alkaline conditions.

Sugarcane bagasse amendment improves the quality of green waste vermicompost and the growth of Eisenia fetida

Vermicomposting is a feasible method for disposing of lignocellulosic waste while generating a useful product.The current study assessed the potential of vermicomposting green waste mixed with sugarcane bagasse in proportions of 25%,50%,and 75%(v:v,based on dry weight).The suitability was evaluated based on the agrochemical properties,earthworm biomass,and phytotoxicity.The final vermicomposts exhibited near-neutral pH values(7.1-7.6),and lower EC values(0.43-0.72 mS/cm)and C:N ratios(14.1-19.9).The content of available nutrients and CEC for all the vermicomposts exceeded those of the control compost(without earthworms).For vermicomposts,the average values of NO3-N,AP,AK,and CEC were 53,517,1362 mg/kg,and 158 cmol/kg,respectively.The total contents of heavy metals increased in all vermicompost treatments compared to control composts with the following average final percentages:Zn(2.0%),Cr(15.5%),Pb(23.4%),and Cu(44.3%),but these amounts were safe for application in agroforestry.The addition of sugarcane bagasse to green waste significantly increased the content of total humic substance,humic acid and urease activity,acid and alkaline phosphatase activity,and Eisenia fetida reproduction.The addition of 25%sugarcane bagasse to green waste decreased the toxicity to germinating seeds.These results revealed that vermicomposting is a feasible way to degrade green waste into a value-added chemical product.

Sintering of solid waste generated in iron and steel manufacturing process in Shougang Jingtang

It is important to make full use of waste generated in the iron and steel manufacturing process for energy saving,emission reduction,low carbon production and a circular economy.Based on research on different kinds of industrial solid wastes from Shougang Jingtang,wastes have been optimized for use in sintering.At first,basic tests for all kinds of solid wastes that may be used in sintering were carried out,including chemical composition,calorific value of a fuel,holding time at high temperatures,the sintering pot test,etc.The results show that the appropriate solid waste ratios for current sintering conditions are：steel slag〈5%,scale 2.0%,environmental ash 2.0%,and cyclone ash 1.0%;blast furnace dry ash,sintering electric field ash,and steelmaking ash should not be circulated in sintering.As for the fuel structure,both coking ash and nut coke should be below 15%.By optimizing the addition of solid wastes,the damage of harmful elements to sintering and blast furnaces has been significantly reduced,which satisfies the demands for blast furnace materials and earns benefits.The utilization of solid wastes has made a contribution to the circular economy and sustainable development.

Environment and economic feasibility of municipal solid waste central sorting strategy： a case study in Beijing

Although Beijing has carried out municipal solid waste （MSW） source separation since 1996, it has largely been ineffective. In 2012, a ＂Green House＂ program was established as a new attempt for central sorting. In this study, the authors used material flow analysis （MFA） and cost benefit analysis （CBA） methods to investigate Green House＇s environment and economic feasibility. Results showed that the program did have significant environmental benefits on waste reduction, which reduced the amount of waste by 34%. If the Green House program is implemented in a residential community with wet waste ratio of 66%, the proportion of waste reduction can reach 37%. However, the Green House is now running with a monthly loss of 1982 CNY. This is mainly because most of its benefits come from waste reduction （i.e., 5878 CNY per month）, which does not turn a monetary benefit, but is instead distributed to the whole of society as positive environmental externalities. Lack of government involvement, small program scale, and technical/managerial deficiency are three main barriers of the Green House. We, thus, make three recommendations： involve government authority and financial support, expand the program scale to separate 91.4 tons of waste every month, and use more professional equipment/technologies. If the Green House program can successfully adopt these suggestions, 33.8 tons of waste can be reduced monthly, and it would be able to flip the loss into a profit worth 35034 CNY.

Efects of solution chemistry on arsenic(V) removal by low-cost adsorbents

Natural and anthropogenic arsenic （As） contamination of water sources pose serious health concerns, especially for small communities in rural areas. This study assessed the applicability of three industrial byproducts （coal fly ash, lignite, and green waste compost） as the low-cost adsorbents for As（V） removal under various field-relevant conditions （dissolved oxygen, As（V）/Fe ratio, solution pH, and presence of competing species）. The physico-chemical properties of the adsorbents were characterized by XRD, XRF, FT-IR, and NMR analysis. Batch experiments demonstrated that coal fly ash could provide effective As（V） removal （82.1%-95%） because it contained high content of amorphous iron/aluminium hydroxides for As（V） adsorption and dissolvable calcium minerals for calcium arsenate precipitation. However, the addition of lignite and green waste compost was found unfavourable since they hindered the As（V） removal by 10%-42% possibly due to dissolution of organic matter and ternary arsenate-iron-organic matter complexes. On the other hand, higher concentrations of dissolved iron （comparing As（V）/Fe ratios of 1：1 and 1：10） and dissolved oxygen （comparing 0.2 and 6 mg/L） only marginally enhanced the As（V） removal at pH 6 and 8. Thus, addition of dissolved iron, water aeration, or pH adjustment became unnecessary because coal fly ash was able to provide effective As（V） removal under the natural range of geochemical conditions. Moreover, the presence of low levels of background competing （0.8 or 8 mg/L of humic acid, phosphate, and silicate） imposed little influence on As（V） removal, possibly because the high adsorption capacity of coal fly ash was far from exhaustion. These results suggested that coal fly ash was a potentially promising adsorbent that warranted further investigation.