Salinity, organic content, micronutrients and heavy metals in pig slurries from South-eastern Spain

The increase in commercial pig production is an opportunity to reuse animal manures in arid and semiarid soils as a source of nutrients and organic matter. However, there are components in pig slurry that are potentially dangerous for the environment. In this study, pig slurries of 36 pig farms in South-eastern Spain were evaluated for salt content (electrical conductivity, chloride and sodium), organic load (BOD5 and COD), micronutrients (Fe, Cu, Mn and Zn), and heavy metals (Cd, Co, Cr, Ni and Pb). Except for electrical conductivity, Cu and Zn, components in pig slurries did not vary considerably between animal production stages, indicating similar management of diverse animal types. Assuming an application rate based on the maximum input of nitrogen from animal manure (210 kg total N/ha/yr), the estimates for soil annual load of Cl and Na, 415 kg/ha, could be a significant salinisation risk. Cu and Zn seemed to be the metals that could be accumulated most in soils where application of pig slurries is common (4 and 15 kg/ha/yr, respectively). The estimated heavy metal (Cd, Co, Cr, Ni and Pb) input to soils would be 260 g/ha/yr, with a relative contribution of Cr>Ni>Pb>Co>Cd.     

Higher pH and faster decomposition in biowaste composting by increased aeration

Composting of source separated municipal biowaste has at several plants in Scandinavia been hampered by low pH. In this study the hypothesis that increased aeration would improve the process was tested in full-scale experiments at two large composting plants. The O2 concentrations were high (>15%) even at the low aeration rates, so the prevailing low pH was not due to an anaerobic process environment. In spite of this, increased aeration rates at the start of the process resulted in higher microbial activity, increased pH and a more stable compost product. At one plant the decomposition rate varied in proportion to the aeration rate, to the extent that the temperatures and O2 concentrations were similar during the early processes even though aeration rates varied between 10 and 50 m3/(h, m3 compost). However, increased aeration caused severe drying of the compost, but at one plant the addition of water was adequate to prevent drying. In conclusion, by increasing the aeration rates and adding water to compensate for drying, it was possible to shorten the time needed to produce a stable compost product and thus to increase the efficiency of the composting plants.     

Solid waste management in Abuja, Nigeria

The new city of Abuja provided an opportunity to avoid some of the environmental problems associated with other major cities in Africa. The current status of solid waste management in Abuja has been reviewed and recommendations for improvements are made. The existing solid waste management system is affected by unfavourable economic, institutional, legislative, technical and operational constraints. A reliable waste collection service is needed and waste collection vehicles need to be appropriate to local conditions. More vehicles are required to cope with increasing waste generation. Wastes need to be sorted at source as much as possible, to reduce the amount requiring disposal. Co-operation among communities, the informal sector, the formal waste collectors and the authorities is necessary if recycling rates are to increase. Markets for recycled materials need to be encouraged. Despite recent improvements in the operation of the existing dumpsite, a properly sited engineered landfill should be constructed with operation contracted to the private sector. Wastes dumped along roads, underneath bridges, in culverts and in drainage channels need to be cleared. Small-scale waste composting plants could promote employment, income generation and poverty alleviation. Enforcement of waste management legislation and a proper policy and planning framework for waste management are required. Unauthorized use of land must be controlled by enforcing relevant clauses in development guidelines. Accurate population data is necessary so that waste management systems and infrastructure can be properly planned. Funding and affordability remain major constraints and challenges.     

Development of a new quality fair access best value performance indicator (BVPI) for recycling services

Recycling schemes are being used worldwide to reduce the impact of municipal waste. Those using public funds are usually obliged to set performance indicators by which the standards of such schemes can be measured. In the UK, a set of statutory Best Value Performance Indicators (BVPI) must be reported annually, such as the Quality of Fair Access, which monitors the public's access to recycling facilities within 1000 m (known as BVPI 91). This work shows that BVPI 91, and performance indicators like it, quantify only very basic recycling services. A much more sensitive performance indicator is developed in this paper, labelled as the Maximum Practicable Recycling Rate Provision (MPRRP) achievable by a local authority. It indicates the percentage of local waste that could be reasonably recycled using the services provided, calculated on the basis of the average composition of the local waste, the local population coverage for collection of any materials, and nationally provided information stating how much of each material stream is generally suitable (practical) for recycling. Evidence for the usefulness of this new quantity is presented. Although this paper refers a particular performance indicator in the UK, its findings are applicable to all urban areas worldwide needing to monitor recycling service. Furthermore, the MPRRP could be used for planning purposes, and for determining the level of performance of an existing service, by comparing its predicted recycling rate to that actually obtained. Further work is now being carried out on this.     

Simultaneous treatment of PVC and oyster-shell wastes by mechanochemical means

This work presents a new process for dechlorinating poly-vinyl chloride (PVC) by the use of oyster-shell waste. The process consists of milling of PVC waste with oyster-shell waste, followed by washing the milled sample with water. The milling of PVC and oyster-shell mixture results in size reduction and rupture in bonds, leading to mechanically induced reactions between the two to form CaCl2 and hydrocarbon with C=C bonds. Washing the milled mixtures with water at room temperature allows complete removal of chlorine from the milled sample. More than 95% of chlorine in PVC was removed when 2h grinding is conducted for the mixture. The present process could offer a potential route to the handling and disposal of oyster-shell and PVC wastes.     

Studies on acidification in two-phase biomethanation process of municipal solid waste

Biomethanation of municipal solid waste (MSW) is a slow process and the yield of biogas is usually low. Enhancement of acidification is necessary to increase the biogas yield in biomethanation of MSW. MSW contains a significant fraction of ligno-cellulosic material. The acidification of these materials influences the biogas yield. In the present study, hydrolysis and acidification have been considered as a combined phase. Experiments have been conducted to study the effect of recirculation of leachate on the acidification stage of the two-phase biomethanation process. Chemical oxygen demand (COD) and volatile fatty acid (VFA) were considered as indicator parameters. The study was also conducted to investigate the effect of using acid and alkali solution of 0.1% concentration in the acidification study. It was observed that daily recirculation of leachate does not have any major impact on the acidification process. It was also observed that treatment of MSW with sodium hydroxide yields leachate of significantly higher COD and VFA values compared to others.     

Bioleaching of metals from spent lithium ion secondary batteries using Acidithiobacillus ferrooxidans

Bioleaching of spent lithium ion secondary batteries, containing LiCoO2, was attempted in this investigation. The present study was carried out using chemolithotrophic and acidophilic bacteria Acidithiobacillus ferrooxidans, which utilized elemental sulfur and ferrous ion as the energy source to produce metabolites like sulfuric acids and ferric ion in the leaching medium. These metabolites helped dissolve metals from spent batteries. Bio-dissolution of cobalt was found to be faster than lithium. The effect of initial Fe(II) concentration, initial pH and solid/liquid (w/v) ratio during bioleaching of spent battery wastes were studied in detail. Higher Fe(II) concentration showed a decrease in dissolution due co-precipitation of Fe(III) with the metals in the residues. The higher solid/liquid ratio (w/v) also affected the metal dissolution by arresting the cell growth due to increased metal concentration in the waste sample. An EDXA mapping was carried out to compare the solubility of both cobalt and lithium, and the slow dissolution rate was clearly found from the figures.     

Leachability and metal-binding capacity in ageing landfill material

In order to study the stability of landfilled heavy metals, landfill material from a combined household and industrial waste landfill was aerated for 14 months to simulate the natural ageing processes as air slowly begins to penetrate the landfill mass. During aeration, the pH of the landfill material decreased from around 8.6 to 8.1 and the carbon content also decreased. In order to investigate the possible fate of metals in ageing landfills, a four-stage sequential extraction technique was applied. The ability of the materials to bind metal ions by electrostatic attractions and to form stronger complexes was studied separately. The amount of exchangeable cations, the capacity to bind metal ions by electrostatic attraction and the capacity of the landfill material to complex copper ions were increased by the aeration process. However, results from the sequential analysis showed an increased solubility of sulphur and some metals (Cd, Co, Cu, Ni and Zn). Equilibrium speciation models (Medusa) indicated that the organic matter deposit had a significant capacity to bind metal ions provided that pH was sufficiently high. However, as carbonates are consumed over time, the risk for metal mobility increases. Therefore, the landfills can become an environmental risk, depending on variations in the solubility of metal ions due to changes in pH, redox status and the availability of organic material.     

Architects' perspectives on construction waste reduction by design

The construction, demolition and excavation waste arising in England was estimated at 91 million tonnes in 2003. The current thinking on construction waste minimisation is heavily focussed on several issues relating to physical construction waste and recycling guides. Indeed, much had been published on ways to improve on-site waste management and recycling activities but very few attempts made to address the effect of design practices on waste generation. However, there is a consensus in the literature that the architect has a decisive role to play in helping to reduce waste by focussing on designing out waste. This paper examines previous studies on architects' approach towards construction waste minimisation; and by means of a postal questionnaire, investigates: the origins of waste; waste minimisation design practices in the UK; and responsibilities and barriers within the UK architectural profession. The findings reveal that waste management is not a priority in the design process. Additionally, the architects seemed to take the view that waste is mainly produced during site operations and rarely generated during the design stages; however, about one-third of construction waste could essentially arise from design decisions. Results also indicate that a number of constraints, namely: lack of interest from clients; attitudes towards waste minimisation; and training all act as disincentives to a proactive and sustainable implementation of waste reduction strategies during the design process.     

Evaluation of leaching and extraction procedures for soil and waste

Laboratory leaching tests may be used for source term determination as a basis for risk assessment for soil-groundwater pathways on contaminated sites. In order to evaluate different leaching procedures, batch extraction tests and percolation tests were performed using three reference materials produced from contaminated soil, demolition waste and municipal solid waste incinerator bottom ash. Emphasis was placed on the investigation of the leachability of the heavy metals copper and chromium, polycyclic aromatic hydrocarbons (PAHs) and the anions chloride and sulfate. Significant discrepancies between column experiments and batch/extraction tests were found for the release of PAHs and to a lesser extent for the heavy metals Cu and Cr. Additionally interlaboratory comparisons were conducted based on different leaching tests with the reference materials and evaluated using the criteria of comparability and reproducibility. The best reproducibility was achieved for all investigated substances in column tests. The reproducibility of batch tests was acceptable except for PAHs. The results from the experimental work will help establish standardized and feasible laboratory procedures as fundamental for substance specific risk assessment of contaminated sites.