Kinetics and thermodynamic studies of Methyl Orange removal by polyvinylidene fluoride-PEDOT mats

We report the preparation of poly(3,4-ethylene dioxythiophene) (PEDOT)-modified polyvinylidene fluoride electrospun fibers and their use as a novel adsorbent material for the removal of the anionic dye Methyl Orange (MO) from aqueous media. This novel adsorbent material can be used to selectively remove MO on a wide pH range (3.0–10.0), with a maximum capacity of 143.8 mg/g at pH 3.0. When used in a recirculating filtration system, the maximum absorption capacity was reached in a shorter time (20 min) than that observed for batch mode experiments (360 min). Based on the analyses of the kinetics and adsorption isotherm data, one can conclude that the predominant mechanism of interaction between the membrane and the dissolved dye molecules is electrostatic. Besides, considering the estimated values for the Gibbs energy, and entropy and enthalpy changes, it was established that the adsorption process is spontaneous and occurs in an endothermic manner. The good mechanical and environmental stability of these membranes allowed their use in at least 20 consecutive adsorption/desorption cycles, without significant loss of their characteristics. We suggest that the physical-chemical characteristics of PEDOT make these hybrid mats a promising adsorbent material for use in water remediation protocols and effluent treatment systems.     

Carbonization of waste PVC to develop porous carbon material without further activation

Efficient removal of chlorine from PVC achieved by two-stage heat-treatment (280 and 410 degrees C) provided chlorine-free isotropic pitch containing additive. The pitch was stabilized and carbonized into porous carbons with surface areas of approximately 300 m2/g. Resultant porous carbons showed three pore structures of supermicropore, micropore and mesopore. The generation of CO2 from the decomposition of the CaCO3 additive in waste PVC is responsible for the development of porous structures. The surface area of the carbonized product increased after the removal of CaO.     

Municipal solid waste management in the Southern Province of Sri Lanka: problems, issues and challenges

This paper describes the problems, issues and challenges faced by Sri Lanka based on the outcome of a recent study conducted in the country's Southern Province. The study consists of a public survey, discussions with local authority staff involved in waste management, discussions with Provincial Council and Government officials, dialogue with local politicians, review of documents and field observations. The study revealed that only 24% of the households have access to waste collection and that in rural areas it was less than 2%. A substantial number of households in areas without waste collection expect local authorities to collect their waste. The study also showed that most sites in the province are under capacity to handle any increased demand. Urgent and immediate improvement of the waste disposal sites is necessary to meet the current demand for improved waste collection. The study also revealed that there is a high willingness of people for home composting.     

A GIS based transportation model for solid waste disposal--a case study on Asansol municipality

Uncontrolled growth of the urban population in developing countries in recent years has made solid waste management an important issue. Very often, a substantial amount of total expenditures is spent on the collection of solid waste by city authorities. Optimization of the routing system for collection and transport of solid waste thus constitutes an important component of an effective solid waste management system. This paper describes an attempt to design and develop an appropriate storage, collection and disposal plan for the Asansol Municipality Corporation (AMC) of West Bengal State (India). A GIS optimal routing model is proposed to determine the minimum cost/distance efficient collection paths for transporting the solid wastes to the landfill. The model uses information on population density, waste generation capacity, road network and the types of road, storage bins and collection vehicles, etc. The proposed model can be used as a decision support tool by municipal authorities for efficient management of the daily operations for transporting solid wastes, load balancing within vehicles, managing fuel consumption and generating work schedules for the workers and vehicles. The total cost of the proposed collection systems is estimated to be around 80 million rupees for the fixed cost of storage bins, collection vehicles and a sanitary landfill and around 8.4 million rupees for the annual operating cost of crews, vehicles and landfill maintenance. A substantial amount (25 million rupees/yr) is currently being spent by AMC on waste collection alone without any proper storage/collection system and sanitary landfill. Over a projected period of 15 yr, the overall savings is thus very significant.     

The effect of sodium chloride on the dissolution of calcium silicate hydrate gels

The use of cement based materials will be widespread in the long-term management of radioactive materials in the United Kingdom. One of the applications could be the Nirex reference vault backfill (NRVB) as an engineered barrier within a deep geological repository. NRVB confers alkaline conditions, which would provide a robust chemical barrier through the control of the solubility of some key radionuclides, enhanced sorption and minimised corrosion of steel containers. An understanding of the dissolution of C-S-H gels in cement under the appropriate conditions (e.g., saline groundwaters) is necessary to demonstrate the expected evolution of the chemistry over time and to provide sufficient cement to buffer the porewater conditions for the required time. A programme of experimental work has been undertaken to investigate C-S-H gel dissolution behaviour in sodium chloride solutions and the effect of calcium/silicon ratio (C/S), temperature and cation type on this behaviour. Reductions in calcium concentration and pH values were observed with samples equilibrated at 45 degrees C compared to those prepared at 25 degrees C. The effect of salt cation type on salt-concentration dependence of the dissolution of C-S-H gels was investigated by the addition of lithium or potassium chloride in place of sodium chloride for gels with a C/S of 1.0 and 1.8. With a C/S of 1.0, similar increases in dissolved calcium concentration with increasing ionic strength were recorded for the different salts. However, at a C/S of 1.8, anomalously high calcium concentrations were observed in the presence of lithium.     

A kinetic analysis of solid waste composting at optimal conditions

Six municipal solid waste (MSW) and yard waste components (food waste, mixed paper, yard waste, leaves, branches, grass clippings) were aerobically decomposed to measure the extent of decomposition under near optimal conditions. Decomposition was characterized by at least two principal stages, for most components, as was indicated by the carbon dioxide production rates. An aerobic biodegradation conceptual model is presented here based on the principle that solids hydrolysis is the rate-limiting step during solid waste composting. The mineralizable solid carbon of each solid waste component was assumed to comprise the readily, the moderately and the slowly (or refractory) hydrolysable carbons, each hydrolyzing at different rates to aqueous (water soluble) carbon. Aqueous carbon mineralizes to CO2 at rapid rates that are not rate-limiting to the process. Solids hydrolysis rate constants were calculated after fitting the experimentally determined carbon dioxide production rate data to model results. Hydrolysis rates for the readily hydrolysable carbon in all components ranged from approximately 0.06 to 0.1 d(-1); hydrolysis rates for the moderately hydrolysable carbon ranged from 0.005 to 0.06 d(-1). Leaves, branches and grass clippings did not have a readily hydrolysable carbon fraction, whilst the leaves and branches had the largest slowly hydrolysable carbon fractions (70%, 82%, respectively, of the total solid organic carbon). Grass and yard waste did not contain slowly hydrolysable carbon fractions. Food waste had the largest readily hydrolysable carbon fraction and produced the highest amount of CO2 among all substrates. Moderately hydrolysable solid carbon fractions ranged from 16% to 90% of the total solid organic carbon for all substrates used.     

The Influence of Chironomus plumosus Larvae on Nutrient Fluxes and Phosphorus Fractions in Aluminum Treated Lake Sediment

One of the methods to diminish the internal phosphorus (P) loading is inactivation of P by aluminum (Al). After addition of Al to lake water an Al(OH)₃ floc is formed, which settles to the bottom and initially form a lid on the sediment surface. The effects of Chironomus plumosus larvae on sediment nutrient fluxes and P binding-sites in the sediment after addition of Al were tested. C. plumosus larvae were added to sediment cores in which sediment–water fluxes of nutrients were measured four times. After one month, the sediment was sectioned with depth and P fractions were measured by sequential chemical extraction. The chironomids created burrows through the Al layer which caused a significantly increased efflux of P from the Al treated sediment, because the P had only limited contact to the added Al. The chironomids also affected the P fractions in the sediment by their bioturbating activity. Thus, they caused increased Al concentrations in the upper part of the Al treated sediment. This created an enhanced contact between Al and P in the upper 7 cm of the sediment and, as a result, an increased binding of P to Al and a lowered porewater P. The DIP efflux is therefore expected to be lowered after the initial phase. Al had no effects on the nitrogen fluxes, but the chironomids enhanced the release, and decreased the release or increased the uptake by the sediments.     

Modelling Phosphorus Retention in Lakes and Reservoirs

Steady-state models for the prediction of P retention coefficient (R) in lakes were evaluated using data from 93 natural lakes and 119 reservoirs situated in the temperate zone. Most of the already existing models predicted R relatively successfully in lakes while it was seriously under-estimated in reservoirs. A statistical analysis indicated the main causes of differences in R between lakes and reservoirs: (a) distinct relationships between P sedimentation coefficient, depth, and water residence time; (b) existence of significant inflow–outflow P concentration gradients in reservoirs. Two new models of different complexity were developed for estimating R in reservoirs: , where τ is water residence time (year), was derived from the Vollenweider/Larsen and Mercier model by adding a calibrated parameter accounting for spatial P non-homogeneity in the water body, and is applicable for reservoirs but not lakes, and , where [P_in] is volume-weighted P concentration in all inputs to the water body (μg l⁻¹), was obtained by re-calibrating the OECD general equation, and is generally applicable for both lakes and reservoirs. These optimised models yield unbiased estimates over a large range of reservoir types.     

Changes in soil characteristics and plant species composition along a moisture gradient in a Mediterranean pasture

Soil physicochemical characteristics, total aboveground biomass, number of species and relative abundance of groups and individual species were measured along a moisture gradient in a pasture, flooded in part during winter through early summer, adjacent to Pamvotis lake in Ioannina, Greece. Soil and vegetation measurements were conducted in 39 quadrats arranged in four zones perpendicular to the moisture gradient. The zone closest to the lake, recently separated from the lake, became part of the pasture and its soil texture was quite different from that of the other zones with a substrate containing 91% sand. Except for pH, this zone had the lowest values in the other five soil physicochemical characteristics measured (organic matter, total and extracted inorganic nitrogen, Olsen extracted phosphorus and extractable potassium); in the other zones organic matter, total nitrogen, phosphorus and potassium tended to increase from the driest to the wettest zone. Total aboveground biomass, ranging from 280 to 840 gm-2, is high for herbaceous pastures in the conditions of Mediterranean climate and it was not related to distance from the lake's shoreline, although the highest values were measured at intermediate distances, or to any of the various soil characteristics measured. Also, the number of species/0.25 m2 was not related to any of the various soil characteristics, but it was highest at the intermediate distances from the lake's shoreline. Species composition varied along the moisture gradient. Forbs as well as annual grasses and legumes declined in abundance from the driest to the wettest places; the reverse was the case for sedges and perennial grasses and legumes. These results indicate that the soil moisture gradient was the principal factor affecting soil characteristics and plant species composition. Since most species were recorded in all the four zones of the pasture, indicating that these can tolerate all variations in abiotic conditions of pasture, the vegetation zonation seems to be influenced by competition. Each functional group of species tends to dominate in a particular range of the soil moisture gradient where it is better suited and tends to exclude competitively other species. Management practices (mowing and grazing) affect the kinds of processes which maintain the observed community structure either by preventing the establishment of later successional species, like reeds and woody species, or by moderating the shoot competition, especially in the wetter zones, and thus permitting the creeping species to grow successfully.     

The effects of leachate recirculation with supplemental water addition on methane production and waste decomposition in a simulated tropical landfill

In order to increase methane production efficiency, leachate recirculation is applied in landfills to increase moisture content and circulate organic matter back into the landfill cell. In the case of tropical landfills, where high temperature and evaporation occurs, leachate recirculation may not be enough to maintain the moisture content, therefore supplemental water addition into the cell is an option that could help stabilize moisture levels as well as stimulate biological activity. The objectives of this study were to determine the effects of leachate recirculation and supplemental water addition on municipal solid waste decomposition and methane production in three anaerobic digestion reactors. Anaerobic digestion with leachate recirculation and supplemental water addition showed the highest performance in terms of cumulative methane production and the stabilization period time required. It produced an accumulated methane production of 54.87 l/kg dry weight of MSW at an average rate of 0.58 l/kg dry weight/d and reached the stabilization phase on day 180. The leachate recirculation reactor provided 17.04 l/kg dry weight at a rate of 0.14l/kg dry weight/d and reached the stabilization phase on day 290. The control reactor provided 9.02 l/kg dry weight at a rate of 0.10 l/kg dry weight/d, and reached the stabilization phase on day 270. Increasing the organic loading rate (OLR) after the waste had reached the stabilization phase made it possible to increase the methane content of the gas, the methane production rate, and the COD removal. Comparison of the reactors' efficiencies at maximum OLR (5 kgCOD/m(3)/d) in terms of the methane production rate showed that the reactor using leachate recirculation with supplemental water addition still gave the highest performance (1.56 l/kg dry weight/d), whereas the leachate recirculation reactor and the control reactor provided 0.69 l/kg dry weight/d and 0.43 l/kg dry weight/d, respectively. However, when considering methane composition (average 63.09%) and COD removal (average 90.60%), slight differences were found among these three reactors.