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

Silk is composed of two major proteins, fibroin (fibrous protein) and sericin (globular, gumming protein). Fibroin has been used in textile manufacturing and for several biomaterial applications, whereas sericin is considered a waste material in the textile industry. Sericin has recently been found to activate the proliferation of several cell-lines and has also shown various biological activities. Sericin can form a gel by itself; however, after mixing with other polymers and cross-linking it can form a film or a scaffold with good characteristics that can be used in the cosmetic and pharmaceutical industries. Sericin is proven to cause no immunological responses, which has resulted in a more acceptable material for biological applications.

Bacterial population dynamics were examined during bioremediation of an African soil contaminated with Arabian light crude oil and nutrient enrichment (biostimulation). Polymerase chain reaction followed by denaturing gradient gel electrophoresis (DGGE) were used to generate bacterial community fingerprints of the different treatments employing the 16S ribosomal ribonucleic acid (rRNA) gene as molecular marker. The DGGE patterns of the nutrient-amended soils indicated the presence of distinguishable bands corresponding to the oil-contaminated–nutrient-enriched soils, which were not present in the oil-contaminated and pristine control soils. Further characterization of the dominant DGGE bands after excision, reamplification and sequencing revealed that Corynebacterium spp., Dietzia spp., Rhodococcus erythropolis sp., Nocardioides sp., Low G+C (guanine plus cytosine) Gram positive bacterial clones and several uncultured bacterial clones were the dominant bacterial groups after biostimulation. Prominent Corynebacterium sp. IC10 sequence was detected across all nutrient-amended soils but not in oil-contaminated control soil. Total heterotrophic and hydrocarbon utilizing bacterial counts increased significantly in the nutrient-amended soils 2 weeks post contamination whereas oil-contaminated and pristine control soils remained fairly stable throughout the experimental period. Gas chromatographic analysis of residual hydrocarbons in biostimulated soils showed marked attenuation of contaminants starting from the second to the sixth week after contamination whereas no significant reduction in hydrocarbon peaks were seen in the oil-contaminated control soil throughout the 6-week experimental period. Results obtained indicated that nutrient amendment of oil-contaminated soil selected and enriched the bacterial communities mainly of the Actinobacteria phylogenetic group capable of surviving in toxic contamination with concomitant biodegradation of the hydrocarbons. The present study therefore demonstrated that the soil investigated harbours hydrocarbon-degrading bacterial populations which can be biostimulated to achieve effective bioremediation of oil-contaminated soil.

This paper uses the ‘lens’ of integrated and sustainable waste management (ISWM) to analyse the new data set compiled on 20 cities in six continents for the UN-Habitat flagship publication Solid Waste Management in the World’s Cities. The comparative analysis looks first at waste generation rates and waste composition data. A process flow diagram is prepared for each city, as a powerful tool for representing the solid waste system as a whole in a comprehensive but concise way. Benchmark indicators are presented and compared for the three key physical components/drivers: public health and collection; environment and disposal; and resource recovery – and for three governance strategies required to deliver a well-functioning ISWM system: inclusivity; financial sustainability; and sound institutions and pro-active policies. Key insights include the variety and diversity of successful models – there is no ‘one size fits all’; the necessity of good, reliable data; the importance of focusing on governance as well as technology; and the need to build on the existing strengths of the city. An example of the latter is the critical role of the informal sector in the cities in many developing countries: it not only delivers recycling rates that are comparable with modern Western systems, but also saves the city authorities millions of dollars in avoided waste collection and disposal costs. This provides the opportunity for win–win solutions, so long as the related wider challenges can be addressed.

To investigate the influence of semi-aerobic and anaerobic landfill operation on stabilization processes of landfill sites with leachate recirculation, in situ simulated semi-aerobic landfill sites with leachate recirculation (SLR) and anaerobic landfill sites with leachate recirculation (ALR) were constructed. Refuse properties and landfill settlement were determined. Leachate quality and landfill gas compositions were monitored regularly. Based on the data obtained, leachate quality, landfill gas and final refuse characteristics were adopted as assessment factors to quantitatively evaluate stabilization of landfill sites. The results showed that volatile solids (VS), total organic carbon (TOC) and biologically degradable matter (BDM) of aged refuse in SLR (15.8, 7.3 and 9.9%, respectively) were lower than those in ALR, which were 19.1, 9.2 and 11.3%, respectively. Settlement and reduction ratio of SLR were 1.71 m and 30.91%, respectively, and 1.40 m and 25.45% in the case of ALR. Concentrations of organic pollutants, especially ammonia, were reduced in SLR, and variation in leachate quality was also smoother than ALR. Throughout the experiment the average concentration of CH₄ in ALR was higher than that in SLR (36.7 and 14.5%, respectively). At the end of the experiment, SLR was moderately stable, while ALR was moderately unstable. The comprehensive assessment index (I) for SLR and ALR was 200 and 355, respectively.

In India the exotic epigeic species, Eisenia fetida is mostly used for vermicomposting. The introduction of exotic species into local bio system may affect the indigenous earthworm species population. A comparative study between exotic species (Eisenia fetida) and indigenous species Perionyx sansibaricus and Perionyx excavates was performed to determine the potential of indigenous species of the area vis-à-vis the exotic species for composting of domestic organic waste blended with cattle manure. The results of the study show a significant reduction in initial C/N ratio from 55 to 13 for P. excavates and 15 for P. sansibaricus of the ready product which was within the agronomic acceptable limit ( < 20). The total organic matter reduced by 50% and pH also reduced to be nearer to neutral, but there was an increase in total nitrogen to 102% and total phosphorus increased from the initial concentration of 7.62 g kg⁻¹ up to 13.2 g kg⁻¹. Overall, by employing above indigenous species, domestic organic waste can be directly converted into high-quality hygienic stable fertilizer (vermicompost) which is rich in nitrogen, phosphorus and potassium and free from pathogens.

The measurement of vertical gas diffusivity and permeability of compacted municipal solid waste (MSW) using an analytical gas flow and transport model was evaluated. A series of pressure transducers were buried in a MSW landfill and in situ pressures were modelled using an algorithm that predicts soil-gas pressures based on field-measured barometric pressure data and vertical diffusivity. The vertical gas diffusivity that represented the best-fit of the measured pressures was estimated at 20 locations and ranged from 0.002 to 0.052 m² s⁻¹. The vertical gas permeability ranged from 3.3 × 10⁻¹⁴ to 4.5 × 10⁻¹² m² for the upper-most 3 to 6 m of compacted MSW. The shortfalls of applying this method to landfill conditions are also discussed.

Many of the characteristics of typical medical waste ash can be found by using ash leaching experiments. The present study investigated the characteristics of fly ash derived from incineration of medical waste in China. The particle diameter of the fly ash was in the range 154–900 μm. Elemental analyses of the fly ash indicated that it contained calcium, aluminium, iron, sodium, potassium and magnesium, and that copper, lead, chromium and mercury were the dominant heavy metals it contained. As leaching time was increased the leaching concentrations of the heavy metals increased and the leaching toxicity was augmented. When the pH was neutral, the concentrations of most heavy metals in the leachate were minimum whereas when the pH was alkali or acid, the leaching toxicity was greatly enhanced. High temperature melting was found to be a good method of fixing heavy metals, and the main components of the sinter were Fe₃O₄, SiO₂, CaSO₄ and CaSiO₃, etc.

Metallurgical wastes – oxygen converter sludge, dust from cast iron production, lead matte, and slag from recycling of used lead batteries – were treated with Acidithiobacillus bacteria. Bacterial activity and adaptability on waste and some waste mixtures were investigated. Acidithiobacillus bacteria may easily attack oxygen converter sludge, lead matte and slag and affect the mobility of metals. Cast iron dust is not a suitable substrate for applied bacteria due to the absence of reduced sulfur and reduced iron in its mineralogical composition. Nevertheless, the pure culture was able to adapt to the mixture of this waste with slag. Disposal of these metallurgical wastes deserves special attention due to potential attack by microorganisms and consequent pH changes. According to subsequent release of hazardous substances to the environment, this phenomenon can lead to evident environmental risks.

State parks are highly sensitive areas of great natural importance and tourism value. Herein a case study involving a basic survey of solid waste which was carried out in 2006 in Agua Blanca State Park, Macuspana, Tabasco, Mexico with two sampling periods representing the high and low tourist season is presented. The survey had five objectives: to find out the number of visitors in the different seasons, to consider the daily generation of solid waste from tourist activities, to determine bulk density, to select and quantify sub-products; and to suggest a possible treatment. A daily average of 368 people visited the park: 18 862 people in 14 days during the high season holiday (in just one day, Easter Sunday, up to 4425 visitors) and 2092 visitors in 43 days during the low season. The average weight of the generated solid waste was 61.267 kg day⁻¹ and the generated solid waste average per person was 0.155 kg person⁻¹day⁻¹. During the high season, the average increased to 0.188 kg person⁻¹day⁻¹ and during the low season, the average decreased to 0.144 kg person⁻¹day⁻¹. The bulk density average was 75.014 kg m⁻³, the maximum value was 92.472 kg m⁻³ and the minimum was 68.274 kg m⁻³. The sub-products comprised 54.52% inorganic matter; 32.03% organic matter, 10.60% non-recyclable and 2.85% others. Based on these results, waste management strategies such as reuse/recycling, aerobic and anaerobic digestion, the construction of a manual landfill and the employment of a specialist firm were suggested.

A method is proposed that uses operations research techniques to optimize the routes of waste collection vehicles servicing dumpster or skip-type containers. The waste collection problem is reduced to the classic travelling salesman problem, which is then solved using the Concorde solver program. A case study applying the method to the collection system in the southern zone of Buenos Aires is also presented. In addition to the typical minimum distance criterion, the optimization problem incorporates the objective of reducing vehicle wear and tear as measured by the physics concept of mechanical work. The solution approach, employing graph theory and mathematical programming tools, is fully described and the data correction process is also discussed. The application of the proposed method minimized the distance travelled by each collection vehicle in the areas studied, with actual reductions ranging from 10 to 40% of the existing routes. The shortened distances led in turn to substantial decreases in work done and therefore in vehicle wear and tear. Extrapolation of the results to the entire southern zone of Buenos Aires indicates potential savings for the civic authorities of more than US$200 000 per year in addition to the qualitative impacts of less traffic disruption, less vehicle driver fatigue and less pollution.