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The paper starts by reviewing the increasing production of waste and the growing importance of its thermal treatment, which aims at volume reduction of the waste, at the destruction, capture, and concentration of hazardous substances, and at the recovery of energy (WtE).

The combustion of poultry litter, which is rich in phosphorus, in a fluidized bed combustor (FBC) is associated with agglomeration problems, which can lead to bed defluidization and consequent shutdown of the installation. Whereas earlier research indicated coating induced agglomeration as the dominant mechanism for bed material agglomeration, it is shown experimentally in this paper that both coating and melt induced agglomeration occur. Coating induced agglomeration mainly takes place at the walls of the FBC, in the freeboard above the fluidized bed, where at the prevailing temperature the bed particles are partially molten and hence agglomerate. In the ash, P2O5 forms together with CaO thermodynamically stable Ca3(PO4)2, thus reducing the amount of calcium silicates in the ash. This results in K/Ca silicate mixtures with lower melting points. On the other hand, in-bed agglomeration is caused by thermodynamically unstable, low melting HPO4 2and H2PO4salts present in the fuel. In the

The oversupply of organic fertilizers causes an urgent need for alternative treatments of manure. CO2 neutral electricity is produced from poultry manure, a renewable fuel which is relatively dry and has a heating value of 6-8 MJ/kg. The electricity production from manure saves emissions from fossil fuel combustion, resulting in a reduced environmental impact in the impact category climate change. Moreover, as manure contains a large amount of ammoniacal N, and due to nitrification and denitrification processes, land spreading of poultry manure causes larger emissions of NH3, N2O and NOx than combustion. Electricity production from manure therefore outperforms land spreading in the impact categories terrestrial acidification, particulate matter formation, marine eutrophication and photochemical oxidant formation. The fluidized bed combustor of BMC in the Netherlands generates zero waste, as the ash is recovered as a PK fertilizer, which is odorless, dry, sterile and has a lower mass and volume than the manure, making it more suitable for export to regions with a high P demand. The ash causes however technological problems, such as agglomeration and deposition.

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Thermal valorization of biomass or waste in a fluidized bed combustor may result in agglomeration of the bed material, coated with ash, potentially causing defluidization. In this paper, the causes of agglomeration for various fuels are critically reviewed, based on thermodynamic grounds. It is shown that even for phosphorus rich biomass types, in most cases the largest melt phase consists of alkali silicates: Ca phosphates are formed instead of Ca silicates, leading to lower melting points in the CaO-K2O-SiO2 system. Although thermodynamic optimization of the four main ash forming elements (K, Ca, Si and P) only provides an estimate of the amount of melt phase, it is shown that for various fuels the agglomeration behavior can be explained consistent with experimental findings from literature. As a consequence, for most biomass and waste types a similar thermodynamic estimation can be made to predict agglomeration problems and incorporate countermeasures in the design and operation of the fluidized bed combustor.

The amount of different persistent organic pollutants (POPs) in the input of waste incinerators was compared to that in the output. Three cases were considered: a rotary kiln incinerating hazardous waste, a grate furnace incinerating municipal solid waste (MSW) and the same grate furnace co-incinerating plastics of waste of electrical and electronic equipment (WEEE) and automotive shredder residue (ASR) with MSW. The mass balance for PCBs in the rotary kiln indicates that these POPs are destroyed effectively during incineration. The grate furnace can be a sink or source of PCDD/Fs and PCBs depending on the concentrations in the incinerated waste. In order to compare the total amount of POPs in input and output, a methodology was developed whereby the amount of POPs was weighed according to minimal risk doses (MRDs) or cancer potency factors. For both incinerators the PCDD/Fs, PCBs and polyaromatic hydrocarbons (PAHs) are the main contributors to total weighed POP output. In MSW, the PCDD/Fs, PBDD/Fs and polybrominated diphenylethers (PBDEs) are the main contributors to the weighed POP input. The ratios of the weighed POP-input over -output clearly indicate that the rotary kiln incinerating hazardous waste is a weighed POP sink. The grate furnace incinerating MSW is a weighed POP sink or source depending on the POP-concentrations in the waste, but the difference between output and input is rather limited. When e.g. ASR and plastics of WEEE, containing high concentrations of PBDEs and PCBs, are co-incinerated in the grate furnace, it is clearly a weighed POP sink.

The presence of heavy metals in concentrations above legal limit values is one of the main obstacles preventing closure of the phosphorus (P) cycle through directly applying wastewater treatment sludge ash as a fertilizer. Therefore, an alternative procedure is proposed to recover the valuable P from the sludge ash via wet chemical extraction. This comprehensive study uses several inorganic and organic acids, chelating agents and an alkaline solution to establish optimal and cost-effective conditions for wet P extraction from sludge ash. The optimization takes into account co-extraction of the following heavy metals: Cd, Cr, Cu, Ni, Pb and Zn. Design of experiments results show extraction liquid concentration, liquid/solid ratio and contact time all affect P and heavy metal extraction efficiency, both individually and through interaction. In addition, type of extraction liquid and pH at the end of the extraction procedure also affect P and heavy metal extraction efficiency. Combining results of XRD and SEM-EDX analysis with extraction data shows that at a pH < 2, both Ca-and Al-phosphates in the ash dissolve easily. However, at slightly higher pH only Ca-phosphates dissolve well and at alkaline pH only Al-phosphates. The best trade-off between high P extraction, low heavy metal co-extraction and low operational costs is obtained with H 2 SO 4 (0.5 N, 10 ml/g, 120 min) and oxalic acid (0.5 N, 12.8 ml/g, 120 min). H 2 SO 4 outperforms the other extraction liquids in terms of extraction liquid costs per kg P extracted, whereas extraction with oxalic acid results in the lowest heavy metal co-extraction, thus reducing the downstream processing costs. None of the extraction liquids considered is appropriate for heavy metal removal prior to P extraction due to loss of P and insufficient heavy metal removal.