Stabilization of Waste-to-Energy (WTE) fly ash for disposal in landfills or use as cement substitute.

This study investigated two approaches for managing Waste-to-Energy (WTE) fly ash (FA): (i) phosphoric acid stabilization of FA and disposal in non-hazardous landfills, so that it can pass the U.S. TCLP procedure and meet the U.S. Resource Conservation and Recovery Act (RCRA) standards; (ii) use of FA or phosphoric acid stabilized fly ash (PFA) as cement substitute in construction for avoiding disposal in landfills and reducing the consumption of Portland cement. The effect of stabilization was identified by TCLP tests and XRD quantification (QXRD), which showed that the economically optimal concentration for PFA to pass the RCRA was 1 mol/L H3PO4 (equivalent to 0.4 mol of H3PO4/kg of FA). Zn/Pb-phosphates were formed in treated ash by using high concentration H3PO4 (e.g., 3 mol/L). Thus, the hazardous FA was chemically stabilized to PFA, that were both discussed as cement substitute. QXRD and SEM results showed that both FA and PFA (1 mol/L H3PO4) chemically reacted with cement and water. Up to 25 vol% of the cement can be replaced by FA or PFA, with similar mechanical performance of cement mortars than that of reference. Testing by LEAF Method 1313-pH dependence showed that the FA and PFA cement mortars exhibited the same leachability of heavy metals; therefore, this study demonstrated the technical feasibility of utilizing either raw FA or stabilized PFA as supplementary cementitious material. The leachability of heavy metals in optimal FA or PFA 25 vol% cement mortar was under the U.K. WAC non-hazardous limits.

Materials and energy recovery at six European MBT plants.

Mechanical Biological Treatment (MBT; called "dirty" Materials Recovery Facilities in the U.S.) is a waste management method, developed mostly in Europe, which combines sorting of recyclable materials (metals, paper, plastics, glass) with composting/digestion of green/ food wastes and, in some cases production of a fuel material. In 2018-19, the authors visited six MBT facilities in Europe that use different approaches for the recovery of materials and energy from mixed MSW. These plants were studied with respect to feedstock composition, operating conditions, capital expenditure, financial viability and environmental impacts. The compost product of most facilities examined did not comply with agricultural standards and, therefore, it was classified as compost-like output (CLO) and used as daily cover in landfills. The best composting practice used source separated organic materials (yard and other green wastes) and yielded a marketable compost. MBT plants that did not include the recovery of fuel materials had lower landfill diversion rates and, also, lower capital and operating costs. It was concluded that an MBT plant must include a very efficient sorting and recyclables recovery line and charge a sufficient gate fee. Also, in addition to the recycled products, there should be a stream to recover fuel materials sent to a power plant or cement plant, thus increasing revenue, and landfill diversion, and maximizing greenhouse gas (GHG) savings.

The status of waste management and waste to energy for district heating in South Korea.

This paper focuses on waste management and waste to energy (WTE) for district heating in S. Korea. The chemical formula for the materials disposed of in volume base waste fee (VBWF) bags that are processed in WTE plants was calculated as: C6H9.9O2.3, with a heat of formation of 27.6 MJ/kg. The average heating value for the 35 WTE plants was 9.7 MJ/kg, and the average amount of energy recovered was calculated at 1.5 MWh/ton waste processed. 22 of the 35 WTE plants comply with the limits of the R1 formula for energy recovery plants (R1 > 0.61), as introduced by the EU. It was estimated that 8% of the district heating demand is provided by WTE in S. Korea. WTE plants can contribute to about 0.6% to the total electricity demand of S. Korea and aid the efforts of the nation to phase out the dependence on fossil fuels. The average dioxin emissions of all WTE plants were 0.005 ng TEQ/Nm3 (limit:0.1 ng TEQ/Nm3), and most of the other pollutants examined indicated a ten-fold to hundred-fold lower emissions than the national and the EU standards. S. Korea indicated an improved performance in sustainable waste management, with combined recycling/ composting and WTE rates of about 80%, as compared to the average of the EU-28 with 65%, and the US with 36.5%, even if the EU and the US had higher GDP/capita (PPP) than S. Korea.

Major sources of mercury emissions to the atmosphere: The U.S. case.

In 1989, the two major sources of mercury emissions to the atmosphere in the U.S. were coal-fired power plants (80 tons Hg) and waste to energy power plants (82 tons Hg). This paper examines what has happened to these two major sources of mercury emissions since 1989. A comparison within the waste management industry is, also, provided. The 2014 total anthropogenic emissions of mercury in the U.S. were 51.8 t. The results of the analysis of emissions by industrial sector showed that the largest source of anthropogenic mercury were coal-fired power plants. Among industrial processes, the ferrous metals recycling and the cement industries were the largest emitters of mercury. With regard to waste-to-energy power plants, all of which, since the nineties, have installed advanced emission control systems, the results have been very satisfactory: The authors obtained mercury emission data from operators of most of the waste-to-energy (WTE) power plants in the US. The results showed that in 2014 the 77 U.S. WTE plants in total emitted 0.4 tons of mercury, corresponding to 0.77% of the U.S. total. This number was one half of that reported by the National Emissions Inventory (NEI) for "municipal waste combustion'' (0.64 t) due to the fact that the NEI survey included incinerators without energy recovery. A 2002 Earth Engineering Center study had shown that the mercury emissions of the U.S. WTE industry decreased from 81.8 t in 1989 to 2.2 t in 2001. The present study showed that between 2001 and 2014 the U.S. WTE industry mercury emissions were reduced further, by a factor of seven.