Albert Koenig

Escalating trends in the urban metabolism of Hong Kong: 1971-1997

Abstract Urban metabolism measures quantitatively a citys load on the natural environment. We update the Newcombe et al. (3) pioneering study of Hong Kongs urban metabolism in 1971, highlighting trends in resource consumption and waste generation. Per capita food, water and materials consumption have surged since the early 1970s by 20%, 40%, and 149%, respectively. Tremendous pollution has accompanied this growing affluence and materialism, and total air emissions, CO2 outputs, municipal solid wastes, and sewage discharges have risen by 30%, 250%, 245%, and 153%. As a result, systemic overload of land, atmospheric and water systems has occurred. While some strategies to tackle deteriorating environmental quality have succeeded, greater and more far-reaching changes in consumer behavior and government policy are needed if Hong Kong is to achieve its stated goal of becoming “a truly sustainable city” in the 21st century.

Autotrophic denitrification of landfill leachate using elemental sulphur

One of the most economical means of nitrogen removal from leachate is biological treatment by nitrification, followed by heterotrophic denitrification. An alternative biological denitrification process is autotrophic denitrification using Thiobacillus denitrificans . This autotrophic bacteria oxidizes elemental sulphur to sulphate while reducing nitrate to elemental nitrogen gas, thereby eliminating the need for addition of organic carbon compounds. For this study, pilot-scale elemental sulphur packed bed columns with fixed-film denitrification have been selected as the most suitable treatment process. The effect of hydraulic retention time as well as the effect of concentration and loading rate of nitrate on nitrate removal efficiency as a function of sulphur particle size were determined. The results indicate that (i) autotrophic denitrification can effectively remove nitrate from synthetic and actual nitrified leachate at concentrations much higher than hitherto reported; (ii) the minimum hydraulic retention time necessary for complete denitrification depends on sulphur particle size; (iii) the maximum area loading rate, in g NO 3 − -N/m 2 ·d, appears to be the process limiting factor and is practically independent of sulphur particle size; and (iv) the observed stoichiometric relationships compare well with those previously reported.

Physical properties of dewatered wastewater sludge for landfilling

In the context of landfilling dewatered wastewater sludge in Hong Kong, with landfills up to 140 m high, one of the most significant properties of sludge is its physical nature with regard to moisture characteristics and associated geotechnical stability. Commonly, lower limits are set on total solids content, but no geotechnical stability criteria are applied with the exception of Germany where a minimum requirement for vane shear strength is set at 25 kN/m2. The purpose of this study was to determine and evaluate dewatered wastewater sludge from three Hong Kong municipal wastewater treatment plants with regard to the following physical and geotechnical properties: (i) vane shear strength; (ii) consolidation characteristics such as compression index, compressibility factor, coefficient of consolidation and compressibility coefficient; and (iii) hydraulic characteristics such as permeability and intrinsic resistance. Although dewatered sludge exhibits quite different characteristics as compared to soils, predictive logarithmic relationships may be established between various properties which are consistent with the critical state model for soils, conventional filtration and consolidation theory. Such representation provides a valuable basis for understanding the sludge characteristics and behaviour to landfill design.

Ecosystem appropriation by Hong Kong and its implications for sustainable development

Abstract The Hong Kong Special Administrative Region is a highly developed modern city where technical and economic advances have made it possible to support 7 million people on 120 km2 of built-up land, resulting in 58 000 people per km2, one of the highest population densities in the world. This population depends on a continual supply of materials, energy and information to function, and these resources are mainly supplied from outside Hong Kongs own geographical boundaries. The ecological footprint (EF) of Hong Kong due to its direct and indirect consumption of renewable resources and waste generation is presented. Additionally, the paper traces the spatial patterns of Hong Kongs EF and examines the implications of this ecosystem appropriation. The study finds an EF for Hong Kong of about 6 ha per capita, with the largest appropriation occurring for marine ecosystems. If the impacts of fish farming are included, Hong Kong appropriates a marine area nearly 2000 times its own built-up city area. Current resource consumption and waste generation patterns in Guangdong, China — where much of Hong Kongs terrestrial ecosystem appropriation occurs — are also discussed.

Effect of air recirculation and reuse on composting of organic solid waste

Abstract Composting has become increasingly popular in the past decade as a biological treatment process of organic solid wastes, generated from different sources, with the purpose of recovery, stabilization and volume reduction of waste material in the form of compost. In this study, the effect of different modes of aeration on composting of solid waste using two heat insulated closed pilot-scale reactors was investigated. The modes of aeration studied were upflow, downflow, alternate upflow/downflow, and internal recirculation in a single-reactor system as well as reuse of spent air in a two-reactor system in series. Composting tests were performed in two stages of 20–30 days duration each. Temperature at different heights of the composting mass as well as air velocity were continuously monitored by a datalogger. Air flow was continuous or intermittent depending on temperature. Oxygen content in the spent air was regularly measured. The results show that (i) the application of unidirectional upflow or downflow aeration creates significant vertical distribution of temperature in the composting mass; and (ii) internal recirculation of air in a single-reactor system and reuse of spent air in a two-reactor system appeared to achieve a more uniform temperature distribution and thereby accelerated degradation of the organic matter. Practical applications in composting plants are discussed.

Kinetic analysis of forced aeration composting- II. Application of multilayer analysis for the prediction of biological degradation

Extensive pilot-scale composting tests for organic solid waste were conducted under different modes of aeration, to investigate vertical temperature distributions and their effect on biological degradation at different heights of the composting mass. The modes of aeration applied were upflow, downflow, alternate upflow/downflow, and internal air recirculation. Temperatures at different heights of the composting mass were continuously monitored. Results show that (i) significant variation in temperature and biodegradable volatile solids (BVS) degradation occur in the composting mass along the vertical direction when unidirectional aeration is applied; (ii) application of alternate upflow/downflow aeration or periodic mixing greatly reduces vertical gradients in temperature and biodegradable volatile solids (BVS) degradation; and (iii) the rate and extent of degradation in different layers of the composting mass can be quantitatively predicted by applying a combination of multilayer analysis and a previously established temperature-dependent first-order reaction model.

Effects of Chelating Agents on Zeta Potential of Cadmium-Contaminated Natural Clay

Abstract The effects of pH, ionic strength, cadmium concentration, and chelating agents on the zeta potential of a natural clay of high acid/base buffer capacity from Shanghai, China were investigated in this study, with a view to enhancing the efficiency of electrokinetic remediation of the cadmium-contaminated clay. An increase in the ionic strength of the background solution or cadmium concentration increases the zeta potential on soil particle surfaces, i.e., less negative. CAIW increases the zeta potential slightly but the effects are not pronounced. EDTA and phosphonates decrease the zeta potentials of soil particle surfaces, thus enhancing forward electroosmotic flow.

Application of self-heating test for indirect estimation of respirometric activity of compost: theory and practice.

The self-heating test is widely adopted at solid waste composting plants as a simple and inexpensive test to determine the biological stability of the produced compost. Among other stability measures, the popularity of the respirometric activity determined by oxygen uptake rate is also increasing. However, the determination of respirometric activity by the respirometer is comparatively complicated and expensive. Therefore, in this study an attempt was made to determine indirectly the respirometric activity, using easily available data from the self-heating test. Experimental and theoretical analysis show that (i) the self-heating test could serve two purposes namely, (a) determination of the stability index of the compost; and (b) indirect estimation of respirometric activity; and (ii) the estimated respirometric activity based on the heat energy balance of the self-heating test compares well with the conventional method and could be used as a stability index for compost.

Application of a simplified mathematical model to estimate the effect of forced aeration on composting in a closed system.

The aeration rate is a key process control parameter in the forced aeration composting process because it greatly affects different physico-chemical parameters such as temperature and moisture content, and indirectly influences the biological degradation rate. In this study, the effect of a constant airflow rate on vertical temperature distribution and organic waste degradation in the composting mass is analyzed using a previously developed mathematical model of the composting process. The model was applied to analyze the effect of two different ambient conditions, namely, hot and cold ambient condition, and four different airflow rates such as 1.5, 3.0, 4.5, and 6.0 m(3) m(-2) h(-1), respectively, on the temperature distribution and organic waste degradation in a given waste mixture. The typical waste mixture had 59% moisture content and 96% volatile solids, however, the proportion could be varied as required. The results suggested that the model could be efficiently used to analyze composting under variable ambient and operating conditions. A lower airflow rate around 1.5-3.0 m(3) m(-2) h(-1) was found to be suitable for cold ambient condition while a higher airflow rate around 4.5-6.0 m(3) m(-2) h(-1) was preferable for hot ambient condition. The engineered way of application of this model is flexible which allows the changes in any input parameters within the realistic range. It can be widely used for conceptual process design, studies on the effect of ambient conditions, optimization studies in existing composting plants, and process control.

Nitrogen flow analysis in Huizhou, South China

Eutrophication due to uncontrolled discharges of nitrogen and phosphorus has become a serious pollution problem in many Chinese rivers. This article analyzes the nitrogen flow in Huizhou City in the East River watershed in south China. The material accounting method was applied to investigate the nitrogen flows related to human activities, which consist of the natural and anthropogenic systems. In Huizhou City, the nonpoint source pollution was quantified by the export coefficient method and the domestic discharge was estimated as the product of per capita nitrogen contribution and population. This research was conducted based on statistical information and field data from 1998 in the Huizhou City. The results indicated that the major nitrogen flows in this area were river loads, fertilizer and feedstuff imports, atmospheric deposition, animal manure volatilization, and processes related to burning and other emissions. In 1998, about 40% of the nitrogen was retained in the system and could result in potential environmental problems. Nitrogen export was mainly by rivers, which account for about 57% of the total nitrogen exported. Comparisons made between the East River and the Danube and Yangtze Rivers show that the unit area nitrogen export was of the same magnitude and the per capita nitrogen export was comparable.