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The USA, China and India are the top three producers of municipal solid waste. The composition of solid wastes varies with income: low-to-middle-income population generates mainly organic wastes, whereas high-income population produces more waste paper, metals and glasses. Management of municipal solid waste includes recycling, incineration, waste-to-energy conversion, composting or landfilling. Landfilling for solid waste disposal is preferred in many municipalities globally. Landfill sites act as ecological reactors where wastes undergo physical, chemical and biological transformations. Hence, critical factors for sustainable landfilling are landfill liners, the thickness of the soil cover, leachate collection, landfill gas recovery and flaring facilities. Here, we review the impact of landfill conditions such as construction, geometry, weather, temperature, moisture, pH, biodegradable matter and hydrogeological parameters on the generation of landfill gases and leachate. Bioreactor landfills appear as the next-generation sanitary landfills, because they augment solid waste stabilization in a time-efficient manner, as a result of controlled recirculation of leachate and gases. We discuss volume reduction, resource recovery, valorization of dumped wastes, environmental protection and site reclamation toward urban development. We present the classifications and engineered iterations of landfills, operations, mechanisms and mining.

Water scarcity is one of the major problems in the world and millions of people have no access to freshwater. Untreated wastewater is widely used for agriculture in many countries. This is one of the world-leading serious environmental and public health concerns. Instead of using untreated wastewater, treated wastewater has been found more applicable and ecofriendly option. Moreover, environmental toxicity due to solid waste exposures is also one of the leading health concerns. Therefore, intending to combat the problems associated with the use of untreated wastewater, we propose in this review a multidisciplinary approach to handle wastewater as a potential resource for use in agriculture. We propose a model showing the efficient methods for wastewater treatment and the utilization of solid wastes in fertilizers. The study also points out the associated health concern for farmers, who are working in wastewater-irrigated fields along with the harmful effects of untreated wastewater. The consumption of crop irrigated by wastewater has leading health implications also discussed in this review paper. This review further reveals that our current understanding of the wastewater treatment and use in agriculture with addressing advancements in treatment methods has great future possibilities.

Calcium oxalate (CaOx) crystals occur as intravacuolar deposits in most angiosperm species. Different functions have been attributed to these crystals, some of which are very speculative, until now. Calcium regulation and homeostasis seem to be the most widespread function of CaOx crystals. Being rich in calcium, these crystals constitute a reserve of calcium for plants. However, despite being bioavailable, this reserve is functional in just a few situations due to the low mobility of calcium for phloem translocation. Therefore, CaOx crystals as a calcium reserve is a paradox because in most cases the reserve cannot be used. However, in most plants, these crystals occur in organs or tissues that will be discarded, which allows the elimination of excess calcium. This suggests that CaOx crystals have a functional role in excess calcium excretion. There is some evidence that, for calcium, this excretory function is relevant for plants since they lack an excretory system dedicated to discarding solid wastes, such as calcium salts.

Landfilling is one of the most widely used methods to reduce the impact on the environment and human health by ensuring the management of solid wastes. For the process in question to be called landfill, the landfill leachate must be controlled and liner impermeability conditions must be provided. For this reason, compacted clay liners (CCL) and geosynthetic clay liners (GCL) with very low hydraulic conductivity are often used as hydraulic barriers in landfills to prevent the risk of leachate mixing with groundwater. However, as a result of various interactions between leachate–clay liners, changes occur in the hydraulic conductivity of the liners. In this review, the change (increase/decrease) in the hydraulic conductivity of the landfill liners caused by the contaminants in the leachate composition and the mechanisms responsible for this change were examined. In addition, deficiencies in the literature on this subject were identified and directions for future studies were presented.

It is a common practice in developing countries and in some regions of Europe that solid wastes generated in households (e.g. plastic beverage packaging and other plastic wastes, textile wastes, fibreboards, furniture, tyres, and coloured-paper waste) are burned in wood- or coal-fired stoves during the winter months. In Europe, the types and volume of municipal waste burned in households is virtually unknown because these activities are illegal and not recorded, with the exception of a few media reports or court cases. Even though particulate emissions from illegal waste burning pose a significant hazard to human health due to the combination of excessive emission factors (EFs) and uncontrolled chemical composition, there is scarce information on the specific EFs for PM10 and polycyclic aromatic hydrocarbons (PAHs) in the scientific literature. In this work, controlled combustion tests were performed with 12 different types of municipal solid waste, and particulate emissions were measured and collected for chemical analysis. Absolute EFs for PM10 and PAHs as well as the benzo(a)pyrene (BaP) toxicity equivalent of the latter are reported for the first time for the indoor combustion of 12 common types of municipal solid waste that are frequently burned in households worldwide. It was found that the PM10 emission factors from the combustion of wood-based waste samples were about twice that of firewood, whereas EFs in the range of 11–82 mg g-1 (a factor of 5–40 times higher than that of dry firewood under the same conditions) were obtained for different types of plastic waste. The latter were also found to emit exceptionally high quantities of PAHs, by a factor of 50–750 more than upon the combustion of dry firewood under the same conditions. Since the more toxic 4–6 ring PAHs were predominant in the particulate emission from plastic waste burning, BaP equivalent toxicity was up to 4100 times higher than that from wood combustion.

Solid wastes from domestic, industrial and agricultural sectors cause acute economic and environmental problems. These issues can be partly solved by anaerobic digestion of wastes, yet this process is incomplete and generates abundant byproducts as digestate. Therefore, cultivating mixotrophic algae on anaerobic digestate appears as a promising solution for nutrient recovery, pollutant removal and biofuel production. Here we review mixotrophic algal cultivation on anaerobic waste digestate with focus on digestate types and characterization, issues of recycling digestate in agriculture, removal of contaminants, and production of biofuels such as biogas, bioethanol, biodiesel and dihydrogen. We also discuss applications in cosmetics and economical aspects. Mixotrophic algal cultivation completely removes ammonium, phosphorus, 17β-estradiol from diluted digestate, and removes 62% of zinc, 84% of manganese, 74% of cadmium and 99% of copper.

Adsorption can be efficiently employed for the removal of various toxic dyes from water and wastewater. In this article, the authors reviewed variety of adsorbents used by various researchers for the removal of malachite green (MG) dye from an aqueous environment. The main motto of this review article was to assemble the scattered available information of adsorbents used for the removal of MG to enlighten their wide potential. In addition to this, various optimal experimental conditions (solution pH, equilibrium contact time, amount of adsorbent and temperature) as well as adsorption isotherms, kinetics and thermodynamics data of different adsorbents towards MG were also analyzed and tabulated. Finally, it was concluded that the agricultural solid wastes and biosorbents such as biopolymers and biomass adsorbents have demonstrated outstanding adsorption capabilities for removal of MG dye.

Using solid wastes (SWs) as backfilling material to fill underground mined-out areas (UMOAs) solved the environmental problems caused by SWs and reduced the backfilling cost. In this study, fly ash (FA), gypsum and steel slag (SS) were used to prepare cement-based composites (CBC). The uniaxial compression, computed tomography (CT) and scanning electron microscope (SEM) laboratory experiments were conducted to explore the macro and micromechanical properties of CBC. The findings showed that the uniaxial compressive strength (UCS) of CBC with a curing time of 7 d could reach 6.54 MPa. The increase of SS content reduced the UCS of CBC, while the gypsum and FA content could increase the UCS of CBC. Microscopic studies have shown that the SS particles in CBC have noticeable sedimentation, and the increase of SS content causes the failure mode of CBC from tensile to tensile-shear. These research results can provide a scientific reference for the preparation of backfilling materials.

Energy primarily comes from fossil fuels, which leads to environmental deterioration through increased carbon dioxide load and other greenhouse gases in the atmosphere. Renewable energy is a cheap alternative, and biomass, like municipal solid wastes (MSWs), can be suitably used for energy production. This paper reviews the impact of variations in MSW composition on its physical, chemical, and lignocellulosic properties. It further illustrates how these properties affect torrefaction products. It was observed that MSW can refer to either a combination of different waste types or independent wastes; hence, there is no standard composition of MSW. The variations in composition are responsible for fluctuating physical, chemical, and lignocellulosic properties. These properties, along with torrefaction process parameters, simultaneously affect the torrefied product, whereas lignocellulosic properties influence the biochar yield, and physical and chemical properties impact calorific value and ash content. Torrefying MSW containing low moisture content yields biochar with a high calorific value. Methods to improve the lignocellulosic properties of MSW have not been studied. Research is needed to assess the possibility of improving biochar yields in MSW by enhancing lignin percentages, possibly through blending MSW. A guide on the best blend combinations and ratios is required. Also, it is crucial to study optimal torrefaction process parameters.

Paste backfilling is an incipient underground mine backfill technology in India. It facilitates maximum use of mill tailings with enhanced stability of the underground workings and minimises rehandling of water, as well as provides bulk disposal of mining solid waste. Binder type and dosage plays an important role in paste backfill performance. This paper highlights environmentally friendly utilisation of solid wastes like lead–zinc mill tailings and lead–zinc smelter fuming furnace slag (FFS) as paste backfilling for an underground metalliferous mine. Various experiments were conducted to study the effect of use of FFS as a fractional replacement for ordinary portland cement (OPC) in paste backfilling. The physico-chemical properties of both the lead–zinc mill tailings and fuming furnace slag (FFS) have been examined. In the first set of experiments, raw slag (FFS) was used for paste backfill preparation and experimentation for uniaxial compressive strength (UCS) development, whereas in the second set of experiments, FFS was crushed to -75 μm (80 wt%) and used for the study. Multiple regression analysis of strength development was also conducted up to fifth order. The regression analysis is in accordance with the strength development and justifies the significance of OPC, crushed fuming furnace slag (CFFS) and waste chemistry on the strength gain with curing time. Use of crushed fuming furnace slag as OPC replacement in paste backfill showed encouraging results of strength development in contrast to raw FFS. Also, the economic analysis revealed that the paste backfilling cost per tonne reduced significantly with slag replacement in the binder phase.