Electrocoagulation technique in enhancing COD and suspended solids removal to improve wastewater quality.

This paper presents a preliminary study for the removal of COD and suspended solids in wastewater treatment by combining magnetic field and electrocoagulation (EC) technology. The experiments were carried out using batch apparatus and setup in the static method. Batch experiments with two monopolar iron (Fe) plate anodes and cathodes were employed as electrodes. Wastewater samples were prepared from milk powder with an initial COD of 1,140 mgL(-1) and suspended solids of 1,400 mgL(-1) and acidic conditions were employed (pH approximately 3). DC current was varied from 0.5-0.8 A and operating times were between 30 and 50 min. The results show that the effluent wastewater was very clear (turbidity approximately 9 NTU) and its quality exceeded the direct discharge standard. The suspended solids and COD removal efficiencies were as high as 30.6 and 75.5%, respectively. In addition, the experimental results also show that the electrocoagulation could neutralise the pH of wastewater.     

Simulation of water and nitrogen dynamics in soils during wastewater applications by using a finite-element model

A mathematical model was developed to simulate water movement, mass transport, and nitrogen transformations in soils during wastewater applications. The model is one-dimensional and based on the Galerkin finite-element method. The submodel of mass transport of nitrogen incorporates the convection-dispersion processes of ammonium and nitrate nitrogen, nitrification, denitrification, ammonium exchange and uptake of ammonium and nitrate ions. The accuracy and validity of the proposed model was examined by comparison with an explicit-implicit finite-difference model results. The model was used for simulation of water and nitrogen dynamics during wastewater application in homogeneous and multi-layered soils under different N concentration, rate, duration and scheduling of application.     

Problem of unity of measurements in ensuring safety of hydraulic structures

Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 1, pp. 14–17, January, 1994.     

Biofilm adaptation to sulfate reduction in anaerobic immobilized biomass reactors sujected to different COD/sulfate ratios.

Various aspects of biofilm adaptation to sulfate reduction in horizontal-flow anaerobic immobilized biomass (HAIB) reactors subjected to increasing sulfate concentrations and different COD/sulfate ratios are presented and discussed. Four bench-scale HAIB reactors filled with vegetal carbon (R1 and R2) and polyurethane foam matrices (R3 and R4) were utilized. Influent sulfate concentrations ranging from 500 to 3000 mg/L were applied at COD/sulfate ratios ranging from 5.0 to 1.7. Reactors R1 and R4 were operated with higher sulfate loads than those applied to R2 and R3. For the same COD/sulfate ratio, the highest sulfate reduction efficiency (approximately 80%) was displayed by the vegetal carbon reactor (R2) subjected to low sulfate loads. According to the results of our molecular biology analyses, the different support materials provided different biomass colonization conditions. The lowest diversity of sulfate-reducing bacteria was found in the HAIB filled with polyurethane foam matrices operating with high sulfate loads.     

Long- and short-term interest rates in 19 countries: Tests of cointegration and parameter instability

This paper examines the long-run relationship between short-term and long-term interest rates (both nominal and real) in 19 countries, and explores the possibility that the relationship is statistically stable using Lc, MeanF, and SupF statistics suggested by Hansen [1992]. Empirical results obtained from various cointegration techniques (Johansen, Phillips and Hansen, Stock and Watson, and Park) and quarterly data (1973–1998) show considerable support for the expectations hypothesis in all countries (except the United Kingdom). In a majority of cases, it is also found that a stable relationship exists between the short-term and long-term interest rates.     

Impact of the US–EC price war on major wheat exporters' shares of the Chinese market

China is both the world's largest producer and consumer of wheat. In an attempt to gain a larger slice of the important Chinese market, both the European Community and the United States have offered China subsidised wheat. In addition, other exporters have offered attractive credit arrangements to China. The objective of this paper is to measure the overall impact of these policies on each exporter's share of the Chinese market. To that end, an improved version of the constant market shares model is applied to data on Chinese wheat imports in the 1980's. The results indicate that the United States has been outperforming the other exporters since subsidised US wheat sales were authorised for China in 1987. The implications of the analysis for the smaller exporters and international wheat trade are discussed.     

The transformation of aluminium species in the processes of coagulation, sedimentation and filtration.

The aluminium toxicity is closely related to aluminium species. In this work aluminium was fractionated into seven forms: Al(T), Al(Sus), Al(C + S), Al(S), Al(C), Al(O) and Al(I). Four Al-based coagulants and simulated raw water were used in the laboratory to investigate the aluminium transformation in coagulation, sedimentation and filtration processes. It is the use of Al-based coagulants that contributes more to the increase of the residual aluminium for the low-turbidity raw water, while the Al-based coagulants, especially the polymeric aluminium coagulants, work to remove the aluminium from the high-turbidity raw water. In the case of traditional coagulants, the increase of the turbidity or the dissolved organic carbon (DOC) concentration in the raw water results in a high concentration of Al(C + S). The removal rate of aluminium species in the filtration process is not only related to its size: RAl(Sus) > RAl(C+S), RAl(C) > RAl(S), but also to the physicochemical properties of aluminium species and filter. For the kaolin-polyaluminium chloride system, a lower removal rate of aluminium species results is due to the complexation of humic acid and aluminium species.     

The Changing Status of Collectivized and Private Agriculture under Central Planning

A bstract . Official perceptions of agriculture's role in economic development in the Eastern European Soviet-type economies have undergone significant alterations over the past several decades. These changes have been especially important in Hungary , a country well known for its unorthodox economic approaches. The modifications of status analyzed below have been consistent with the overall economic policy directives of the Communist party, including the current renewed emphasis on economic rationality, pragmatism , and the revitalization of the economic reform of 1968 .