O. Grant Clark

Immobilization of trace metals in contaminated urban soil amended with compost and biochar.

Urban soil amendment with organic matter can increase the steady state concentration of trace metals in urban soil. Different types of organic matter have different abilities to sorb and retain trace metals. The potential of urban soil amended with compost derived from mixed green and table waste and with maple-wood-derived biochar to retain trace metals (Cu, Zn, Cd, Pb) in the presence of de-icing salt (Na) was studied in a leaching test. Soil amended with compost retained significantly higher concentrations of Zn and Pb, as compared to soil amended with biochar, possibly due to the high cation exchange capacity of compost and its positive effect on soil pH. Indicating high ability for retaining trace metals, compost can bind contaminants originating from urban runoff water percolating through urban soil and provide a healthier medium for street tree growth.

Influence of free air space on microbial kinetics in passively aerated compost.

The influence of free air space (FAS) on passively aerated composting has been reported, but the quantitative relationship between FAS and the microbial kinetics in passively aerated compost has not been investigated. This relationship was studied by composting dairy manure and straw in an enclosed, passively aerated, cylindrical vessel. Based on this experimental system, conceptual and numerical models were developed in which the compost bed was considered to consist of layered elements, each being physically and chemically homogeneous. The microbial activity in each layer was represented in order to predict oxygen and substrate consumption and the release of water and heat. Convective transport of air, moisture, and heat through the layers was represented. Microbial growth and substrate consumption rates were described using modified first-order kinetics for each of the mesophilic and thermophilic temperature regimes. The values of the microbial kinetic parameters were adjusted for each layer based on an innovative, non-linear, statistical analysis of temperature histories recorded at different layers in the compost bed during three treatments (i.e., FAS values of 0.45, 0.52, and 0.65). Microbial kinetic rate constants were found to follow a sigmoid relationship with FAS, with correlation coefficients (R(2)) of 0.97 for the mesophilic stage and 0.96 for the thermophilic stage. Temperature histories and airflow measurements from a fourth treatment (FAS value of 0.57) were used as an independent check of the models performance. Simulation results indicate that the model could predict the general trend of temperature development. A plot of the residuals shows that the model is biased, however, possibly because many parameters in the model were not measured directly but instead were estimated from literature. The result from this study demonstrates a new method for describing the relationship between microbial kinetics (k(max)) and substrate FAS, which could be used to improve the design, optimization, and management of passively aerated composting facilities.

Ecosystem biomimetics for resource use optimization in buildings

An ecomimetic method is developed as an innovative and transdisciplinary design approach rooted in the field of biomimetics. This new method emulates the interrelated complexity of the parts of an ecosystem with the intent to design buildings that are more efficient, effective and holistic. Ecomimetics refers to the design of buildings that mimic ecosystem processes and functions. This approach provides potential opportunities for climate change adaptation and mitigation by optimizing the use of resources in buildings. One challenge to the application of ecomimetics in architecture is the lack of systematic methods supported by scientific research, which may prevent development in this field. A theoretical basis and the initial development of an ecomimetic design method is presented, with a description of each step of the design process. Ecological systems are selected for functional properties that match architectural design goals, and then design tools are used to abstract and transfer those properties to architectural systems. The design tools integrated in the method are from the fields of ecological engineering, systems dynamics and architecture. The case of the Eastgate Center in Harare, Zimbabwe, is used to illustrate the method.

Airflow in Passively Aerated Compost

Abstract: Passive aeration systems are more economical than active aeration systems and deliver similar performance, but mathematical descriptions of the process are inadequate for use in its design or optimization. Therefore, a practical analytical model of airflow development in passively aerated compost was developed. The model relates the physical characteristics and temperature of the compost with the predicted passive, convective air flow. The effect of compaction on the permeability of the compost was considered in the application of the model. The model was verified using temperature time series data from a passively aerated composting experiment as inputs, and the calculated results were not significantly different from the measured values (p = 0.97).