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

The final products of the ethanol industry are alcoholic beverages, industrial ethanol and biofuels. They are produced by the same production process, which includes fermentation and distillation of raw materials which come from plant biomass. At the end of the distillation process a waste effluent is obtained called vinasse or stillage. The direct disposal of stillages on land or in groundwater (rivers, streams or lakes), or even for the direct irrigation of crops, pollutes the environment due to their high organic contents, dissolved solids and many other compounds which are toxic or could be contaminants under certain environmental conditions. This work reviews the characterization of vinasses from different feedstock sources and the main treatments for conditioning the soluble solids of vinasses before their disposal.

Three plastics, high density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS), were individually co-pyrolysed with deoiled cake of jatropha (JC) at 400 and 450°C in a batch reactor in the presence of nitrogen under atmospheric pressure to produce modified liquid fractions. At higher temperature (450°C), the yield of liquid fractions by the pyrolysis of plastics (HDPE, PP and PS) alone was found to increase by 11, 12.5 and 11% for HDPE, PP and PS, respectively. Furthermore, the gaseous fraction increased by 1.3 to 2.6% while the residue generation reduced by 12.3 to 15.1%. In comparison with only plastics pyrolysis, the yield of the liquid fraction improved by 2.0 to 4.9% for their co-pyrolysis with JC. Gas chromatography–mass spectrometry analyses demonstrated that the co-processing afforded a reduction of paraffin and olefins in the liquid fractions for all of the experiments. This reduction was found to be in the order of PS > PP > HDPE. Furthermore, the proportion of oxygenates in the liquid product increased in the order of PP > HDPE > PS. Physical characteristics such as oxygenates, water contents, acid values and viscosity increased during the co-pyrolysis of plastics and JC in contrast to the liquid fractions obtained from the pyrolysis of pure plastics. Furthermore, co-pyrolysis offered a reduction in calorific values.

Waste vinegar residue, the by-product of vinegar processing, was used as substrate for phytase production from Aspergillus ficuum NTG-23 in solid-state fermentation to investigate the potential for the efficient re-utilization or recycling of waste vinegar residue. Statistical designs were applied in the processing of phytase production. First, a Plackett–Burman (PB) design was used to evaluate eleven parameters: glucose, starch, wheat bran, (NH₄)₂SO₄, NH₄NO₃, tryptone, soybean meal, MgSO₄·7H₂O, CaCl₂·7H₂O, FeSO₄·7H₂O, incubation time. The PB experiments showed that there were three significant factors: glucose, soybean meal and incubation time. The closest values to the optimum point were then derived by steepest ascent path. Finally, a mathematical model was created and validated to explain the behavioural process after these three significant factors were optimized using response surface methodology (RSM). The best phytase activity was attained using the following conditions: glucose (7.2%), soybean meal (5.1%), and incubation time (271 h). The phytase activity was 7.34-fold higher due to optimization by PB design, steepest ascent path design and RSM. The phytase activity was enhanced 0.26-fold in comparison with the results by the second step of steepest ascent path design. The results indicate that with waste vinegar residue as a substrate higher production of phytase from Aspergillus ficuum NTG-23 could be obtained through an optimization process and that this method might be applied to an integrated system for recycling of the waste vinegar residue.

This study examined the efficiency of different organic waste materials as NPK fertilizer, in addition to the risk for leaching losses related to shower precipitation in the first part of the growing season. The experiment was tested in a pot trial on a sandy soil in a greenhouse. Six organic fertilizers were evaluated: liquid anaerobic digestate (LAD) sourced from separated household waste, nitrified liquid anaerobic digestate (NLAD) of the same origin as LAD, meat and bone meal (MBM), hydrolysed salmon protein (HSP), reactor-composted catering waste (CW) and cattle manure (CM). An unfertilized control, calcium nitrate (CN) and Fullgjødsel® 21-4-10 were used as reference fertilizers. At equal amounts of mineral nitrogen both LAD and Fullgjødsel® gave equal yield of barley in addition to equal uptake of N, P, and K in barley grain. NLAD gave significantly lower barley yield than the original LAD due to leaching of nitrate-N after a simulated surplus of precipitation (28 mm) at Zadoks 14. There was significantly increased leaching of nitrate N from the treatments receiving 160 kg N ha⁻¹ of CN and NLAD in comparison with all the other organic fertilizers. In this study LAD performed to the same degree as Fullgjødsel® NPK fertilizer and it was concluded that LAD can be recommended as fertilizer for cereals. Nitrification of the ammonium N in the digestate caused significantly increased nitrate leaching, and cannot be recommended.

This paper presents the results of the modelling of the biogas extraction in a full-scale Italian landfill by the USEPA LandGEM model and the Andreottola–Cossu approach. The landfill chosen for this research (‘Il Fossetto’ plant, Monsummano Terme, Italy) had accepted mixed municipal raw waste for about 15 years. In the year 2003 a mechanical biological treatment (MBT) was implemented and starting from the end of the year 2006, the recirculation in the landfill of the concentrated leachate coming from the internal membrane leachate treatment plant was put into practice. The USEPA LandGEM model and the Andreottola–Cossu approach were chosen since they require only input data routinely acquired during landfill management (waste amount and composition) and allow a simplified calibration, therefore they are potentially useful for practical purposes such as landfill gas management. The results given by the models are compared with measured data and analysed in order to verify the impact of MBT on biogas production; moreover, the possible effects of the recirculation of the concentrated leachate are discussed. The results clearly show how both models can adequately fit measured data even after MBT implementation. Model performance was significantly reduced for the period after the beginning of recirculation of concentrated leachate when the probable inhibition of methane production, due to the competition between methanogens and sulfate-reducing bacteria, significantly influenced the biogas production and composition.

To ensure quick and uniform aerobic stabilization of biowaste through domestic composting and to prevent malodorous emissions, two modifications were made to a conventional steel barrel composter by: (1) providing 0.0125 m diameter openings throughout the sides and (2) placing a 0.0254 m diameter perforated polyvinyl chloride (PVC) pipe in the middle portion of the barrel. The volume of composting waste before modification of the composting barrel was 40% of the original volume and it was 70%, 4 weeks following the modifications. In addition, the nutrients in the compost were found to be in a more suitable range after modification of the composting barrel. The carbon–nitrogen ratio (C/N) of the compost was in the ideal range of 11–15 in the modified composting reactor but it was quite high (24–25) in the conventional barrel. This modified barrel composting plant proved to be an efficient, eco-friendly, cost-effective solution for the management of organic solid waste materials in developing and technologically less sophisticated countries such as Bangladesh.

The aim of this study was to investigate the engineering applicability of the stratified aged-refuse-based process for landfill leachate treatment. In this work, a pilot-scale (10m³day⁻¹) and a demonstration-scale (200m³day⁻¹) stratified reactor, containing the aged refuse excavated from an 8-year-old closed landfill cell, were used as a medium by which to treat landfill leachate generated in the Shanghai Refuse Landfill (SRL). The preliminary-treated leachate with initial CODcr, NH₃-N and total-N concentrations of 2387–8592, 1431–2145 and 1290–2188 mgL⁻¹, respectively, was intermittently sprayed over the refuse surface eight times a day with 3 h per interval in the pilot study. The results from the pilot operation showed that on average 89.5% of COD, 98.8% of NH₃-N and 52.6% of total N could be removed from a hydraulic load of 0.267–0.444m³m⁻³refuseday⁻¹. Additionally, similar results were observed for the demonstration system even with the leachate of low BOD₅/COD ratios (0.17–0.19). The investment and operational costs of this stratified process were about 20000yuan (€2200) and 1–2 yuan (€0.11–0.22) per m³ leachate treated, respectively. Taken together, the stratified process has some significant advantages including low operation cost, easy maintenance and good adaptability to the leachate of variable quality, which makes this process a viable alternative for the treatment of landfill leachate.

This manuscript develops a model for assessing the time and space variations in unit weight of traditional municipal solid waste (MSW) landfills. The model considers the variations of unit weight caused by deformation of the waste matrix and degradation of the organic portion. Deformation of the waste matrix includes both short-term effects, resulting from mechanical strain during the filling period, and long-term effects, resulting from superposition of waste skeleton creep and waste degradation. Mass loss, caused by waste degradation, not only affects the stress level within the waste column, but also induces large and long-term deformation. Degradation-induced deformation is caused by the local collapse of the solid matrix weakened by mass loss. Considering that the correlation between mass loss and waste deformation is locally erratic and hard to define, a smooth time–strain curve (represented by Kelvin viscoelastic model) is used to describe approximately the overall long-term deformation. The analytical formulation for unit weight is obtained in Laplace transform domain and can be used to simulate spatial and temporal variations of waste unit weight. Unit weight profiles obtained at four MSW landfills using the proposed model agree well with measurements from in situ large-scale unit weight tests. Evolution of unit weight profiles indicates that there is no monotonous varying trend for unit weight along the whole depth of the landfill. Density first increases and then decreases to a stable value in the lower portion, whereas the opposite occurs in the upper portion. Whether unit weight increases or decreases depends on the competition between matrix deformation and degradation processes.

The migration of population towards big cities generates rapid construction activities. These activities not only put pressure on natural resources but also produce construction, renovation and demolition waste. There is an urgent need to find out ways to handle this waste owing to growing environmental concerns. This can reduce pressure on natural resources as well. This paper presents the results of experimental studies which were carried out on hot mix asphalt mixture samples. These samples were manufactured by adding recycled aggregates (RA) with natural crushed stone aggregates (CSA). Three levels of addition of RA were considered in the presented studies. RA were obtained from both the concrete waste of construction, renovation and demolition activities and reclaimed asphalt pavement. Separate samples were manufactured with the coarse and fine aggregate fractions of both types of RA. Samples made with CSA were used as control specimens. The samples were prepared and tested using the Marshall method. The performance of the samples was investigated in terms of density-void and stability/flow analysis and was compared with the performance criteria as given by National Highway Authority for wearing course material in Pakistan. Based on this data optimum asphalt contents were determined. All the samples made by adding up to 50% RA conform to the specification requirements of wearing course material as given by National Highway Authority in terms of optimum asphalt contents, voids in mineral aggregates and stability/flow. A statistical analysis of variation of these samples confirmed that addition is also possible statistically.

There is increasing concern regarding the fate of methyltins in the environment, particularly since large amounts of polyvinyl chloride (PVC) plastics are deposited in landfills. The potential transformation of methyltin chlorides and stannic chloride in landfills was investigated, by incubating the target substances at concentrations relevant to landfill conditions (100 and 500 µg Sn L⁻¹). The amounts of methane formed in all treatment bottles, and controls, were measured to evaluate the general microbial activity of the inocula and possible effects of methyltins on the degradation of organic matter. The methyltins and stannic chloride were found to have no significant inhibitory effects on the activity of landfill micro-organisms, and the methanol used to disperse the tin compounds was completely degraded. In some experimental bottles, the methanol degradation gave rise to larger methane yields than expected, which was attributed to enhanced degradation of the waste material. Alkyltin analyses showed that monomethyltin trichloride at an initial concentration of 500 µg Sn L⁻¹ promoted methylation of inorganic tin present in the inoculum. No methylation activities were detected in the incubations with 100 µg Sn L⁻¹ methyltin chlorides (mono-, di- or tri-methyltin), but demethylation occurred instead. Levels of soluble inorganic tin increased during the incubation period, due partly to demethylation and partly to a release of tin from the waste inocula.