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

A pilot plant-scale composter using simulated solid waste was developed to test the fate of consumer products such as disposable diapers. The simulated waste consisted of a mixture of rabbit chow (which included alfalfa), shredded newspaper, sand, and composted cow manure. The compost mass self-heated from an ambient temperature of 27°C to about 55°C in the first 24 h. Dissolved ammonia levels, high in the early stages of the process, began to decrease after about 4 weeks as nitrate concentration began to increase. Both volatile solids and carbon:nitrogen ratios exhibited gradual decreases with time. Microbial biomass, esterase activity, cellulose mineralization, direct microscopic counts (AODC), and relative APIZYM enzyme activity increased significantly in the first several days, and maintained higher levels than initial measurements throughout the 22-week testing period. We concluded that the simulated solid waste underwent physical, chemical, and microbiological changes that would be expected to occur in municipal solid waste in a full-scale composting system. The pilot plant-scale composter should prove to be a valuable tool in assessing the fate of products and materials under simulated compost conditions.

The successive stages in the composting process of forestry waste from evergreen oak (Quercus ilx sbsp. ballota) were studied under controlled conditions (initial) carbon to nitrogen ratio = 30, T= 27°C). The original material was composted for 6 months and sampled every 15 days. The variables measured on the oak biomass in the course of the experiment showed different kinetics: the weight loss and germination index underwent a monotonic increase whereas the reducing sugars, phenols and E₄₆₅/ E₆₆₅ extinction ratio of the water-soluble fraction stabilized at their lowest values after the first 2 weeks. Other variables, such as alkali solubility, water repellency, pH and particle size, showed maximum or minimum values at intermediate stages of the experiment. In contrast to the adverse agrobiological effects of the direct application to soil of the original waste, germination biotests and greenhouse experiments showed that plant response improved from the 2 first weeks of composting. The kinetics observed for the parameters studied suggested that the less favourable effect on plant yield may come from phytotoxic substances in compost but also from the microbial use of soil N required for the transformation of the most biodegradable compost fractions in special hemicelluloses.

A low cost solution for management of municipal solid waste in small municipalities was investigated; composting experiments were done using domestic waste. Particles > 100 mm were removed, the screened substrate ( < 100 mm) was used for composting experiments on static piles. The results have shown that the size of waste does not affect composting. Though the inert material left greatly adds to the porosity, rainfall does not markedly affect the process; in fact excessive dryness gave the least stable end product, and total nitrogen, ammoniacal nitrogen and phosphorus content were the best pointers to the instability.

Remote sensing is proposed as a useful technique for monitoring landfill sites for gas migration. Landfill gas has the potential to migrate from the site boundaries and cause damage. It is also spatially and temporally very difficult to monitor. The presence of landfill gas in the root zone causes signs of stress to be visible within the vegetation, the stress generally taking the form of chlorosis or dieback. This, in turn, may result in a change in spectral response of the vegetation. Airborne thematic map data and low cost video imagery are proposed as techniques to obtain imagery in order to classify sites according to vegetation stress. A comparison between the efficiency and costs of the two sources of imagery is made. Two case studies are summarized and the economics of the methodology discussed. It is recommended that remote sensing is used in conjunction with soil and geological maps to identify areas of high landfill gas concentration and that this is combined with traditional field measurements to gain a better spatial and temporal understanding of gas migration.

The need for estimating the contaminant concentration of leachates from landfills has rapidly become important because of the increased demand for landfilling, causing serious pollution of water bodies in some places. The present study examines the movement of inorganies from waste into leachate in the course of time. Inorganics are discussed in two groups according to their solubilities in water. The first group of inorganics dissolve immediately in water (i.e. at time t = 0). The inorganic compounds of the second group transfer into water over a longer period of time. The mathematical model is based on a porous and well-mixed medium, and on assumptions of dissolution/dilution and mass transfer according to their infiltration rate. The agreement between theoretical and experimental results from laboratory and literature are investigated. After experimental verification, some mathematical relationships to predict the mass transfer coefficient (k) and maximum concentration (C _max) were also investigated.

This paper describes a research project carried out to investigate the public use of waste recycling banks in Glasgow, U.K. The objective was to find out who was using the banks, and why, and to suggest ways of encouraging more people to use them. Interviews were conducted, with both users and non-users of the banks, at a number of sites in the north-west of the city. The results provided an insight into how the banks were used, what type of people were involved in recycling and what they thought about the operation of the scheme. The reasons given for non-participation were also obtained. A number of conclusions were drawn and recommendations were then made on how to encourage more people to use the banks.