Electroosmotic dewatering of dredged sediments: bench-scale investigation

The Indiana Harbor (Indiana, USA) has not been dredged since 1972 due to lack of a suitable disposal site for dredged sediment. As a result of this, over a million cubic yards of highly contaminated sediment has accumulated in the harbor. Recently, the United States Army Corps of Engineers (USACE) has selected a site for the confined disposal facility (CDF) and is in the process of designing it. Although dredging can be accomplished rapidly, the disposal in the CDF has to be done slowly to allow adequate time for consolidation to occur. The sediment possesses very high moisture content and very low hydraulic conductivity, which cause consolidation to occur slowly. Consolidation of the sediment is essential in order to achieve adequate shear strength of sediments and also to provide enough air space to accommodate the large amount of sediment that requires disposal. Currently, it has been estimated that if a one 3-foot (0.9-m) thick layer of sediment was disposed of at the CDF annually, it would take approximately 10 years to dispose of all the sediment that is to be dredged from the Indiana Harbor. This study investigated the feasibility of using an electroosmotic dewatering technology to accelerate dewatering and consolidation of sediment, thereby allowing more rapid disposal of sediment into the CDF. Electroosmotic dewatering essentially involves applying a small electric potential across the sediment layer, thereby inducing rapid flow as a result of physico-chemical and electrochemical processes. A series of bench-scale electrokinetic experiments were conducted on actual dredged sediment samples from the Indiana Harbor to investigate dewatering rates caused by gravity alone, dewatering rates caused by gravity and electric potential, and the effects of the addition of polymer flocculants on dewatering of the sediments. The results showed that electroosmotic dewatering under an applied electric potential of 1.0VDC/cm could increase the rate of dewatering and consolidation by an order of magnitude as compared to gravity drainage alone. Amending the sediment with polymers at low concentrations (0.5-1% by dry weight) will enhance this dewatering process; however, the optimal polymer concentration and the cost-effectiveness of using polymers should be investigated further.     

Quantifying carbon dioxide and methane emissions and carbon dynamics from flooded boreal forest soil

The boreal forest is subject to natural and anthropogenic disturbances, but the production of greenhouse gases as a result of flooding for hydroelectric power generation has received little attention. It was hypothesized that flooded soil would result in greater CO(2) and CH(4) emissions and carbon (C) fractionation compared with non-flooded soil. To evaluate this hypothesis, soil C and nitrogen (N) dynamics, CO(2) and CH(4) mean production rates, and (13)C fractionation in laboratory incubations at 14 and 21 degrees C under non-flooded and flooded conditions and its effect on labile and recalcitrant C sources were determined. A ferro-humic Podzol was collected at three different sites at the Experimental Lakes Area, Canada, with a high (19,834 g C m(-2)), medium (18,066 g C m(-2)), and low (11,060 g C m(-2)) soil organic C (SOC) stock. Soil organic C and total N stocks (g m(-2)) and concentrations (g kg(-1)) were significantly different (p < 0.05) among soil horizons within each of the three sites. Stable isotope analysis showed a significant enrichment in delta(13)C and delta(15)N with depth and an enrichment in delta(13)C and delta(15)N with decreasing SOC and N concentration. The mean CO(2) and CH(4) production rates were greatest in soil horizons with the highest SOC stock and were significantly higher at 21 degrees C and in flooded treatments. The delta(13)C of the evolved CO(2) (delta(13)C-CO(2)) became significantly enriched with time during decomposition, and the greatest degree of fractionation occurred in the organic Litter, Fungal, and Humic forest soil horizons and in soil with a high SOC stock compared with the mineral horizon and soil with a lower SOC stock. The delta(13)C-CO(2) was significantly depleted in flooded treatments compared with non-flooded treatments.     

WASTE WATER REUSE IN PHOENIX-HOW VIABLE IS IT?1

ABSTRACT: The Phoenix metropolitan area has a unique combination of circumstances which makes it one of the prime areas in the Nation for waste water reuse. Overriding all of these conditions is the long-term inadequacy of the existing water supplies. The Salt River Valley has a ground water overdraft of about 700,000 acre feet per year. To help alleviate this situation, the Corps of Engineers in conjunction with the MAG 208 is looking at ways to reuse a projected 2020 waste water flow of 340,000 acre feet per year. Reuse options identified include ground water recharge, agricultural irrigation, turf irrigation, recreational lakes, fish and wildlife habitats, and industrial cooling. These look nice on paper but before they can be implemented, some hard questions have to be answered, such as: How acceptable are local treatment plants when 15 years ago there was a major push to eliminate local plants; is the Phoenix area ready for reuse in urban areas; what are people willing to pay for water; who benefits if a city goes to ground water recharge; how much agriculture will be left in the area by 2020? These and other questions must be resolved if reuse is to become a viable option in water resource planning in the Phoenix area. Summary. Large scale reuse of waste water conforms with the national goal of better resource management through recycling. The Phoenix metropolitan area has a unique combination of circumstances which makes it one of the prime areas in the nation for waste water reuse. Some of the most notable conditions are: the existence of a large and rapidly growing urban area which is in the process of planning for future waste water management systems; the existence of agricultural areas which are projected to be farmed well into the future, and the existence of constructed and planned major recreational systems such as Indian Bend Wash which can use recycled waste water; the existence of extensive depleted ground water aquifers; the need for a dependable source for the cooling of the Palo Verde Nuclear reactors; and finally, overriding all of this, the long-term inadequacy of the existing water supplies. Given this, one would expect to find total reuse within the Phoenix metropolitan area. Reuse is taking place with irrigation and nuclear power cooling to the west but there is no long term plan which looks at the Valley as a whole and considers waste water as part of the Valley's water resources. The Corps 208 plan is looking at waste water in this manner but initial analysis shows that although reuse is technically feasible there are many financial, social, institutional, and political questions still to be answered. These include: determining the value of existing diminishing water sources and what people are willing to pay for the next source of water; are people willing to identify priority uses of water for the area so that water of varying quality is put to its highest and best use; will the present institutional boundaries remain to create water-rich and water-poor areas; and will legislation be forthcoming to simplify the complex surface and ground water laws that presently exist? The Corps 208 study will not be able to answer these questions, but the goal at the moment is to identify feasible reuse systems along with decisions the public, owners, agencies, and politicians must make to select and implement them. If some sort of logical process is not developed and public awareness not increased, the chance for a long-term plan to utilize waste water as a major element in the Phoenix area water resource picture, may be missed.     

Vegetation changes associated with barrier-dune construction on the outer banks of North Carolina

Manmade dunes are used to stabilize the barrier islands of the mid-Atlantic coast of the United States so that they are more amenable to development. Although this strategy has stabilized extensive sections of the barrier-island substrate, it has also caused significant ecological changes. The rate and pattern of the resulting vegetation changes along the Outer Banks of North Carolina were determined using sequential aerial photography. Successional trends have been altered in favor of more stable woody communities.     

Changing scenario of Himalayan agroecosystems: loss of agrobiodiversity, an indicator of environmental change in Central Himalaya, India

Environmental, biological, socio-cultural and economic variations in the Himalayas have led to the evolution of diverse and unique traditional agroecosystems, crop species, and livestock, which help the traditional mountain farming societies to sustain themselves. During the recent past, as a result of rapid changes in land use caused by socio-cultural and economic changes and various environmental perturbations, the agrobiodiversity of the Central Himalayan agroecosystems has changed steadily. A recent survey conducted in 150 different villages located along an elevated transect of the Alaknanda catchment of the Central Himalaya revealed that over a period of two decades (1970–74 and 1990–94) the cultivated area under many traditional crops had declined significantly. A micro-level study carried out in 30 villages revealed that a series of changes had occurred in land use practices over a period of 25–30 years.The loss of agrobiodiversity and the changing socio-cultural and economic dimensions and their impacts on the sustainability of Himalayan agroecosystems are emerging as major causes of concern at local/regional/national scale, and appropriate options to meet these challenges are discussed in this paper.     

Environmental risk mapping of accidental pollution and its zonal prevention in a city

Accidental releases of pollution can have severe environmental, societal, economic, and institutional consequences. This paper considers the use of risk mapping of accidental pollution events, and zonal prevention measures for alleviating the impact on large urban areas. An Environmental Pollution Accident Risk Mapping (EPARM) model is constructed according to a mapping index system supported by quantitative sub-models dedicated to evaluating the risk arising from different sources of potential accidental pollution. The EPARM approach consists of identifying suitable indexes, assessment of environmental risk at regional and national scales based on information on previous pollution accidents and the prevailing environmental and social conditions, and use of GIS to map the overall risk. A case study of pollution accidents in Minghang District, Shanghai, China is used to demonstrate the effectiveness of the model. The paper also proposes a systemic framework for accidental environmental pollution risk prevention, and detailed countermeasures for specific risk zones.