Waste Management & Research: The Journal for a Sustainable Circular Economy

Some samples of semi-dry flue gas desulfurization (FGD) ash were taken from sinter gas of a steel factory. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were employed to identify the samples in order to investigate their physical and chemical characteristics. The results show that semi-dry FGD ash from a steel factory is stable under atmospheric conditions. It has irregular shape, a smooth surface and loose construction. The size of FGD ash particles is around 0.5—25 µm, the average size is about 5 µm and the median diameter is 4.18 µm. Semi-dry FGD ash from a steel factory consists of CaSO₃, CaSO₄, CaCO₃, some amorphous vitreous material and unburned carbon. An experimental method was found to study the oxidation characteristics of ash. A prediction model of the oxidation efficiency was obtained based on response surface methodology. The results show that not only the temperature, but also gas:solid ratio, play an important role in influencing the oxidation efficiency. The interactions of the gas:solid ratio with temperature play an essential role. An improved response surface model was obtained which can be helpful to describe the degree of oxidation efficiency of semi-dry FGD ash.

Earthworms feed readily upon sludge components, rapidly converting them into vermicompost, reduce the pathogens to safe levels and ingest the heavy metals. Volume is significantly reduced from 1 m³ of wet sludge (80% moisture) to 0.5 m³ of vermicompost (30% moisture). Earthworms have real potential both to increase the rate of aerobic decomposition and composting of organic matter and also to stabilize the organic residues in the sludge — removing the harmful pathogens (by devouring them and also by discharge of antibacterial coelomic fluid) and heavy metals (by bio-accumulation). They also mineralize the essential nutrients nitrogen, phosphorus and potassium from the sludge. It may not be possible to remove toxic substances completely, but at least change the ‘chemical make-up’ of the sludge to make it harmless to the soil and enable its use as a nutritive organic fertilizer. This method has been found to comply with grade A standards for sludge stabilization.

This study focuses on the effect of temperature on the compost quality and the processing time. Two temperature, namely 46°C (high temperature) and 30°C (low temperature) were considered for the composting trials. A mixture of 60% ground corn cob, 30% dried sports grass and 10% bio-activator was used as composting material. The composting process lasted for 120 days. The maturity indices at the end of composting indicate that, for the high-temperature treatment, the compost show an improved quality as compared to the low-temperature treatment. The maturity indices, namely carbon to nitrogen ratio, water extractable organic carbon, ratio of cation exchange capacity to total organic carbon and germination index, determined for the high temperature treatment are: 13.9, 1.48 mg mL ^—1, 2.21, and 86%, respectively. On the basis of the compost characteristics, the processing time for the high- and low-temperature treatments was 75 days and 105 days, respectively. It can be concluded that treatment at the high-temperature level considered in this study presents a more suitable option for improvement of composting.

Laboratory-scale reactors containing mixtures of municipal solid waste and wastewater treatment biosolids were monitored to assess the effect of biosolids on refuse decomposition and on phosphorus (P) cycling and speciation among orthophosphate, acid-hydrolysable P, and organic P. The co-disposal of 10 to 20% (by wet weight) aerobically-digested biosolids with residential refuse was compatible with refuse decomposition although the biosolids did not increase either the maximum methane production rate or the cumulative yield, and did not reduce lag times to the onset of methane production. The results of this study indicated that dissolved reactive phosphorus (DRP) was the dominant dissolved P fraction throughout refuse decomposition and that it was negatively correlated with the methane production rate and pH (r ² = 0.35 for both). P was not found to limit methane production. Biosolids increased dissolved P as well as ammonia-N in some reactors, but this did not have a significant impact on maximum methane production rates. The maximum tolerated Na⁺ and K⁺ concentrations during active methane production were at least 4100 mg Na⁺ L ^—1 and 800 mg K⁺ L^{— 1}, respectively.

A detailed investigation of the development of the mineral composition and crystallinity of fly ash (FA) activated by an integrated process, as well as the relation between that development and phosphate uptake (PU) in solution, was conducted. This process, consisting of pretreatment (mechanical milling), alkali fusion (sodium hydroxide) at 550 °C and acid attack (3 mol L^—1 sulfuric acid), exhibited a remarkable activation effect. One-hour grinding could enhance PU from 0.67 to 1.66 mg PO₄ ^3—-P g ^—1 FA, and then under the optimum chemical conditions with the ratio of NaOH to FA of 0.5 g g^—1 and that of H₂SO₄ to FA of 3 mL g^{— 1}, the PU was further improved to 7.14 mg g^{— 1}. Results also indicated that the PU performance was closely linked with the crystallinity and mineral composition of FA, that is, the treated material with the lowest crystallinity and least crystal phase could achieve the highest PU. For the purpose of destroying original minerals in raw FA farthest and avoiding the production of new crystals, therefore, control on the ratio of NaOH to FA and that of acid to FA was very important during the chemical treatment.

A suspension of sediment from a lagoon in a tap water production plant was collected for this experiment. The suspension was spray dried and calcined at 700 °C for 1 h. After calcining, 30 wt.% of the sediment were mixed with pottery clay. Samples with and without calcined sediment were sintered at 900, 1000 and 1100 °C. The results show that calcined sediment can be used as an additive in pottery clay. The samples with calcined sediment show higher porosity, water absorption and flexural strength, especially for 900 and 1000 °C. At 900 °C, samples with calcined sediment show a porosity of 50% with an average pore size of 68 nm, water absorption of 31% and flexural strength of 12.61 MPa.

Column leaching tests become increasingly important for assessing the risk of release of pollutants from a wide variety of solid materials into water. In this study a column leaching test was designed to provide insight into the fate of selected polycyclic aromatic hydrocarbons (PAHs) in soils and their leaching behaviour. The results showed relatively high initial concentrations of naphthalene, anthracene, and pyrene for column B2. Two proportions of contaminated soil (5 and 20%) used in the columns yielded different leaching behaviour. Different contact time applied in columns B1 and B2 affected the initial amounts of leached PAHs. Results indicated that the distribution pattern of PAH compounds in solid phase considerably affected leached concentrations of PAHs. Released amounts of PAH compounds decreased with increasing molecular size, or rather the hydrophobicity of the compound. The effect of dissolved organic carbon on PAH leaching was also investigated in this study. The mobilization of colloids did not show any significant effect on leached concentrations of PAH compounds. Approximately 4.6 and 2.2% of the total initial amounts of studied PAHs in the soil were leached in columns B1 and B2, respectively. Therefore high PAH concentrations in the solid phase does not imply serious groundwater contamination risk during a leaching event (e.g. raining) and significant amount of contaminants may stay in the soil layer for a long time and do not leach down into groundwater.

In this study, oily sludge samples generated from a Tehran oil refinery (Pond I) were evaluated for their contamination levels and to propose an adequate remediation technique for the wastes. A simple, random, sampling method was used to collect the samples. The samples were analyzed to measure Total petroleum hydrocarbon (TPH), polyaromatic hydrocarbon (PAH) and heavy metal concentrations in the sludge. Statistical analysis showed that seven samples were adequate to assess the sludge with respect to TPH analyses. The mean concentration of TPHs in the samples was 265,600 mg kg^—1. A composite sample prepared from a mix of the seven samples was used to determine the sludge’s additional characteristics. Composite sample analysis showed that there were no detectable amounts of PAHs in the sludge. In addition, mean concentrations of the selected heavy metals Ni, Pb, Cd and Zn were 2700, 850, 100, 6100 mg kg^{— 1}, respectively. To assess the sludge contamination level, the results from the analysis above were compared with soil clean-up levels. Due to a lack of national standards for soil clean-up levels in Iran, sludge pollutant concentrations were compared with standards set in developed countries. According to these standards, the sludge was highly polluted with petroleum hydrocarbons. The results indicated that incineration, biological treatment and solidification/stabilization treatments would be the most appropriate methods for treatment of the sludges. In the case of solidification/stabilization, due to the high organic content of the sludge, it is recommended to use organophilic clays prior to treatment of the wastes.

The ability of rotifers and cladocerans to convert primary to secondary production in wastewaters was tested. Scenedesmus acutus was cultured on Bold’s (defined) medium, wastewater from the tertiary phase of water treatment and a mixture of both. The algal growth rates (µ) ranged from 0.4 to 0.7 day ^—1, being highest in defined medium. The demographic characteristics of Brachionus rubens and Moina macrocopa were tested using algae at a density of 1.0 × 10⁶ cells mL ^—1. Into each test jar, we introduced 20 neonates (< 12-h-old) of either B. rubens or M. macrocopa. Daily (for M. macrocopa) or twice a day (for B. rubens), dead adults and the neonates were enumerated and removed. Average life-span and generation time of B. rubens were not significantly influenced by the algal treatment type. Gross and net reproductive rates were significantly influenced by the medium on which the algae was cultured; in the case of B. rubens, they ranged from 20—36 and 10—22 offspring female^{— 1}; the corresponding values for M. macrocopa were higher (38—110 and 13—31 offspring female^{— 1}, respectively). The rate of population increase was higher for Brachionus (0.41—0.65 day^—1) compared to Moina (0.28—0.57 day^—1). Brachionus had significantly higher growth rates on algae cultured on Bold medium than on treated wastewater while Moina grew significantly better on Scenedesmus cultured on Bold medium or a mixture of treated wastewater and Bold medium than on treated wastewater alone.

The presence of organic materials plays an important role in the fate of heavy metals that are co-disposed together with municipal solid wastes. As a part of an on-going research project, which aims to find out the most effective attenuation mechanism of heavy metal removal in landfills, sorption batch experiments were performed to assess the sorption behaviour of iron, copper, nickel and zinc on synthetic solid wastes containing 76% (W1) and 45% (W2) food waste percentages and waste-to-solution ratios ranging from 1:4 to 1:16. The analysis of sorption data suggested that the data fit a Freundlich equilibrium isotherm. The time required for reaching equilibrium conditions varied for each metal investigated, but all generally reached equilibrium conditions within 7 h. For both solid waste compositions, metal sorption increased with increase in waste-to-solution ratio, with the order of metal removal percentages consistently found to be Zn > Ni > Cu > Fe. The results also show that a large fraction of the heavy metals could be attenuated by sorption on the solid waste. The removal percentages for Zn and Ni were slightly higher for W2, whereas the removal percentages for Fe and Cu were approximately equal for both waste types. Overall, this study demonstrates that sorption is a viable process that can mitigate the potential adverse impacts of landfill leachate.

Coal gangue is a major industrial solid waste in China, causing great environment pollution. According to phase diagram theory, a low-temperature, fast, single-firing body mix for porcelain stoneware tiles was designed in the quaternary system CaO—MgO— Al₂O₃—SiO₂, using coal gangue as the main raw material. The coal gangue was from Baishan city, Jilin province and mainly composed of kaolinite and quartz. Mineralogical compositions and microstructures of some selected samples sintered at different temperatures were identified with X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that the optimal body mix was the one containing 34 wt% coal gangue sintered at 1170°C for about 1 h, with rupture strength of 43 MPa and water absorption of 0.22%. The main crystalline phases of the sintered body were quartz, anorthite and mullite.

In India, the significant increase in the generation of municipal solid waste (MSW) during the last few decades is due to the rapid population and economic development. Though the appropriate attempts are made through the 3-‘R’ principles, waste management still needs to be envisaged seriously by everybody for a cleaner and greener environment. Rag-pickers, who contribute to solid waste management to some extent, are the people who rummage through garbage bins to pick out ‘rags’ for their livelihood. These rag-pickers usually collect the materials that have good re-sale value as these materials are mostly recycled or reused. In the present study, the collection and the management of solid waste and the level of microbial pollution generated through air, soil and solid waste were studied. A questionnaire survey based on age, sex, educational status, socio-economic status, habits and health effects was conducted from 65 randomly selected rag-pickers from various places of Tiruchirappalli city The results revealed that they can be properly educated and trained to protect themselves from unhygienic practices and addiction. Either the Government or non-governmental organizations (NGOs) should devise a suitable proposal to monitor and make use of these unorganized rag-pickers who are indispensable to the society.