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

Organic residues such as sewage sludge, biowastes and composts are increasingly used in land rehabilitation because they can improve the physical, chemical and biochemical properties of soil, and reduce the need for inorganic fertilization. Furthermore, their use contributes to an integrated approach to waste management by promoting recycling of nutrients and minimizing final disposal, especially of organic residues that, due to their composition, can pose problems to agricultural soils. In the present study, three different types of organic residues were considered as amendments to be used in the reclamation of a metal-contaminated mine soil from the Aljustrel mining area (a pyrite mine located in the SW Portugal in the Iberian Pyrite Belt), with high Cu, Pb and Zn total contents: sewage sludge from a municipal wastewater treatment plant (SS), compost from the organic fraction of unsorted municipal solid waste (MSWC), and garden waste compost (GWC), applied at 100 and 200 Mg ha^—1 . The soil and mixtures of soil and amendments were adjusted to 70% of the maximum water-holding capacity determined for each type of sample and incubated in a controlled-temperature room at 20 ± 1 °C. Sub-samples were taken prior to wetting (time zero), and after 7, 14, 21 and 28 days of incubation, and analysed for pH, electrical conductivity, organic matter content, effectively bioavailable Cu, Zn and Pb (extracted with 0.01 mol L^{— 1} calcium chloride) and potentially bioavailable metals (extracted with 0.5 mol L^—1 ammonium acetate, 0.5 mol L ^—1 acetic acid and 0.01 mol L^{— 1} EDTA, pH 4.7). In general, organic residues corrected soil acidity, and increased the total organic matter content of the soil. The SS and the MSWC amendments were roughly equivalent in their ability to correct soil acidity whereas the GWC had the smallest liming capacity and only with 200 Mg ha^—1 GWC did the soil pH reach acceptable values. As expected, all the tested organic residues, at both application rates, were effective in reducing the effectively bioavailable metals in the soil. The Zn bioavailability was the most affected by the addition of organic residues, whereas Pb bioavailability was small even in the unamended soil and was the least affected by treatments. Potentially bioavailable metals increased with SS and MSWC application and the opposite was true following amendment with GWC.

Two experiments were conducted to evaluate the effect of a sewage sludge-based compost (SSC) on the growth and mineral composition of containerized Pinus pinea L. seedlings. In the first experiment, five different substrates were tested: four binary mixtures of SSC and peat (100% SSC, 75% SSC, 50% SSC and 25% SSC, by volume) without fertilization, and a control substrate (peat-based substrate + fertilizer). Seedlings growing in the 100% SSC substrate showed the lowest growth, a consequence of both the low water availability and the high electrical conductivity that made SSC unsuitable to be the only component of a growing-media for pine `seedlings'. The 50% SSC substrate presented physical and chemical properties similar to the control substrate and near the acceptable range for a growing-media. Moreover, no significant differences were found between growth of seedlings from treatment 50% SSC (without mineral fertilization) and seedlings from control treatment (with mineral fertilization). In the second experiment, a fertilization assay was performed with two substrates selected from the first experiment (50% SSC and control). The two substrates were fertilized with three levels of a macronutrient fertilizer (0.5, 1.0 and 2.0 g L ^—1) and two levels of a micronutrient fertilizer (0 and 0.4 g L^—1 of fertilizer containing only micronutrients). Results obtained suggest that replacing 50% (by volume) of peat-based substrate by the sewage sludge-based compost allowed: maintenance of the commercial value of seedlings; reduction of the amount of peat used in the substrate; a need for only half the amount of macronutrient fertilizer applied in the basal fertilization; and omission of micronutrient fertilization.

To study the feasibility of co-composting poultry manure with low quantities of high-value, carbon-rich materials experiments to characterize three pilot-scale piles were carried out. The piles comprised poultry manure (pile 1), poultry manure and straw (pile 2) and poultry manure and sawdust (pile 3), using wood chips as bulking agent. Pile 1 presented the highest losses of organic matter and nitrogen contents (≥ 92.9% and 92.0%, respectively). Although a thermophilic phase (temperature > 40 °C) was not verified for this pile, the final compost was stable (class IV) and free of pathogen indicator micro-organisms but it was the most phytotoxic, and presented a humic and fulvic acids ratio (HA/FA) that was less than 1. In contrast, piles 2 and 3 sustained thermophilic phases and produced stable (class V) and mature (HA/FA > 1) composts. Pile 2 showed the lowest loss in nitrogen content (88.9%) and produced the final compost with the highest C/N ratio (14.7) and the lowest value of electrical conductivity (3.9 mS cm^—1). This study showed that it is possible to reduce the costs of poultry manure composting, namely the costs associated with the use of carbon-rich materials, given that the final co-composts presented parameters within the range of those recommended by the Second Draft Proposal for compost quality.

The effects of three different mixtures of organic waste on composting in a rotary drum were examined by measuring changes in physico-chemical and biological parameters. It was observed that the time courses of the three mixtures: run A (grass cuttings, vegetable waste and food waste), run B (cattle manure, vegetable waste and sawdust) and run C (cattle manure, food waste, vegetable waste, paper waste and sawdust) were quite diverse. Run B, with initial C/N ratio 22 and containing a large proportion of cattle manure produced high quality and mature compost within 20 days. It showed a final total nitrogen (2.1%), final total phosphorus 3.52 g kg^—1, final total organic carbon (TOC) (24.8%) and final moisture content (44%). At the end of 20 days, higher degradation led to final chemical oxygen demand (COD) (454 mg L^{— 1}), biochemical oxygen demand (BOD) (107 mg L^{— 1}), fecal coliform (1.2 × 10² bacteria g^{— 1}), fecal streptococci (85 bacteria g^—1) and low electrical conductivity (1.658 dS m^—1), respectively. Furthermore, run C with initial C/N ratio of 30 and containing a larger amount of food and vegetable waste produced good quality compost and resulted in 4.34% total nitrogen and 2.42% total phosphorus after 20 days, but, it had higher final fecal coliform 2.5 × 10⁴ bacteria g ^—1, fecal streptococci 2.1 × 10⁴ bacteria g^—1, high TOC and NH₄-N and a BOD/COD ratio of 0.63, which rendered it hygienically unsafe and immature. Finally, run A with initial C/N ratio of 15 showed a higher amount of EC (4.84 dS m^—1), NH₄-N, BOD/COD ratio of 0.4 with 15% nitrogen loss, which indicated an unstable product even after 20 days of composting. Therefore, it was found that rotary drum composting of a combination of cattle manure, vegetable waste and sawdust resulted in a primary stabilized compost within 20 days of composting.

Municipal solid waste landfills produce methane, a potent greenhouse gas. A treatment approach is to passively vent landfill gas through a methane-oxidizing biofilter medium, a porous substrate that facilitates the growth of methanotrophic bacteria. Two substrates, compost and a sand—compost—perlite (SCP) mixture, were evaluated in a laboratory-scale experiment for their suitability as biofilter media. The SCP mixture was investigated to minimize settlement and was based on a particle size distribution specification used for turf grass. The long-term (218 days) methane removal rates showed that both compost and SCP were capable of removing 100% of the methane influent flux (134 g CH₄ m ^—2 day^—1). The post-experiment analysis showed that compost had compacted more than SCP. This did not affect the results; however, in a field installation, traffic on the biofilter surface (e.g. maintenance) could cause further compaction and negatively affect performance. Exopolymeric substance produced by the methanotrophic bacteria, attributed by others for declining removal rates due to bio-clogging, was not observed to affect the results. The maximum exopolymeric substance values measured were 23.9 and 7.8 mg D-glucose g^—1 (dry basis) for compost and SCP, respectively.

Shredder residues of end-of-life vehicles and white goods are a complex waste stream, which nowadays most often is disposed of at industrial landfills. This paper describes the most important findings concerning the complex composition of the landfill leachate and its on-site, year-round treatment under cold-climate conditions. A 3-year investigation has confirmed that concentrations of different types of pollutants, most of them at low initial concentrations, can be simultaneously reduced in vertical-flow biofilters consisting of a mixture of peat and carbon-containing ash. For metals such as Mn, Cu, Sn, Cd, Pb, Fe and Ni the average removal was 73, 72, 66, 60, 55, 55 and 37%, respectively. An average reduction of NH₄-N (45%), N_tot (25%), total organic carbon (30%), dissolved organic carbon (28%) and suspended solids (38%) was also obtained. A good reduction was achieved for phenols (between 75 and 95%), polychlorinated biphenyls (between 22 and 99%), and gas chromatography—mass spectrometry amenable pollutants, considered at initial concentration above 50 µg L ^—1 (between 80 and 100%). The performance of the biofilter system was good in spite of large variations of inlet concentration during the considered period.

Demolition waste materials are one of the major industrial waste deposits in many countries and represent an important quantity of potential resources that are not exploited, because the major part of these wastes go to landfill. Indeed, recycling or recovery of demolition waste can reduce the need of primary natural resources. This article gives indicators and a method to analyse demolition waste management with regard to the use of resources contained in these wastes. Demolition wastes are characterized by their contents in energy and raw materials. This content is quantified on the basis of the sum of energy and raw materials necessary for the construction of the building considering the non-renewable character of materials contained in wastes. In fact, this content represents the environmental investment which was necessary to construct the building. An energy balance and a mass balance, with this concept of `raw material and energy' content, can allow a strategy of waste management to be determined in order to salvage the most important parts of energy and raw materials contained in demolition waste, and so identify the strategy which permits a maximum fraction of the initial environmental investment to be saved. Five waste management scenarios concerning building demolition were assessed with this method and these indicators, and the results are presented in this article.

Waste generated from construction and building demolition work constitutes about 68% of all solid waste generated each year in South East Queensland. Consequently, it has created a serious waste management problem. The State Governments of Victoria and New South Wales have been encouraging the use of recycled materials from construction and related waste; they have also promulgated specifications for their use. In Queensland, however, similar regulations are not anticipated in the near future, which explains the lack of funded research conducted in this important arena. This paper presents an evaluation of the prevailing waste recycling practices in Queensland. Nine sites were visited, including two construction sites, three demolition sites, three recycling plants and one landfill in South East Queensland. The difficulties encountered by the recycling programme operators and their associates at these sites are described and the benefits of recycling construction materials are presented. One of the major barriers is that the local councils disallow the use of recycled materials in new construction work. To help rectify these impediments to recycling, recommendations are given to increase the use of recycled construction waste in South East Queensland.

A review of existing industrial processing and results of alternative processing investigations for separating solid mixtures and specifically recycling plastic waste by density separation is presented. Media density separation is shown to be fundamental for separation and/or pre-concentration in the recycling of plastics. The current use of static media processes limits the capacity and size of material that can be treated commercially. Investigations have shown that the hydroscopic properties of plastics can be reduced to improve such separations. This indicates that an alternative processing method is required to increase the commercial recovery of recyclable plastics. Cylindroconical and cylindrical cyclone-type media separators, such as those used for processing coal, are reviewed and suggested as a potential substitute. Both have superior production capacities and are able to process a larger range in particle sizes treated. A summary of results of investigations with cyclone media devices for recycling plastics is presented.

Measuring the performance of solid waste management services usually uncovers very high potential for gains in efficiency and productivity. This circumstance occurs, naturally, due to the fact that these services are outside the market and because they are subjected to various market failures in their organizational framework. The aim of this study was to examine the Portuguese regulatory model and to measure the performance of the Portuguese solid waste management services in order to identify the major reforms carried out and their outcomes. As a first objective, the sunshine regulatory approach adopted in Portugal, in which performance comparison and its public discussion are the main tools, was investigated. The second objective was to compute the efficiency of the Portuguese solid waste management services by means of the non-parametric technique of data envelopment analysis (DEA), evaluating the Portuguese regulatory model and the existing market structure, as well as the influence of the operational environment on efficiency. The benchmarking frontier technique of DEA is particularly useful in the efficiency measurement of public utilities, in which knowledge of the production function is relatively scarce. Several DEA models were used and they all depicted significant inefficiency. The study also proved that efficiency did not depend on ownership (public or private) and that there was no difference in efficiency between the players, irrespective of whether they were regulated or not.