Research Interests
My research interest is in the area of “Organic Waste-to-Resource Recycling via Bioconversion Processes”. The recent and current research projects have the major goal of substantially reducing secondary emissions from the organic waste recycling processes and the resulting products, thus improving the long-term sustainability of waste management. The research projects may be sub-divided into the following bioenvironmental engineering processes and systems, with the multiple purposes of resource recovery and protection of soil, water and air quality.
• Composting and biofertilizer production
• Odor monitoring/Biofiltration for odor control
• Anaerobic fermentation for bioenergy production
Our research involves laboratory-scale and pilot-scale experiments, field studies and modeling of aerobic and anaerobic processes.
Composting and Biofertilizer Production
While composting is becoming a widely adopted bioconversion technology in the holistic approach to solve solid waste management problems, odor and ammonia emissions continue to be significant problems in today's composting practice. Our research is focused on the reduction of these emissions, and the production of a biofertilizer which is more eco-friendly compared to chemical fertilizers in terms of potential surface and groundwater pollution during their use and fossil fuel consumption during their manufacturing.
Preventive means are used for minimizing the odor and ammonia emissions during the active phase of composting, while maximizing nitrogen retention in the finished product. Results of lab studies indicated that it is feasible to convert ammonia to struvite crystals in a wet porous composting matrix ; however, for practical purposes all of the ingredients that make up struvite (N, P and Mg) should be derived from organic wastes rather than as added chemicals. Another component of the project aims at studying the effectiveness of bioadditives in the form of specialized yeast strains and zeolite for biodegrading odors and adsorbing ammonia. Results from lab studies revealed that the addition of yeasts during the curing phase of composting would enhance the compost product, via increased population of beneficial microorganisms and specific enzymes. Evidently, odor level was reduced by 10-30% compared to the control treatment (without pre-conditioning by yeasts) when the finished compost was recycled back to the process as inoculant in the active phase of composting.
Pilot-scale tests of in-vessel and aerated static pile composting systems have been conducted for biosolids from municipal wastewater treatment plants and for crop residues from tomato greenhouses in the Fraser Valley.
Odor Monitoring and Biofiltration for Odor Control
Odors can cause nuisance and health problems. The accurate quantification of odor emission would help government regulatory agencies with a rational approach to respond to odor complaints, and recommend parameters pertinent to odor emission permits for agricultural and industrial facilities. It will also help the industry to assess the effectiveness of odor control devices. In th e research project, total odor concentration is determined via olfactometry and odor panel tests. This odor sensory method remains the most valid for odor evaluation today along with GC/MS techniques, while electronic nose techniques are still being developed for complex odors such as those emitting from composting facilities, landfills and wastewater treatment plants .
The main challenge of olfactometry lies with the variation in the sensitivity and hence judgment of odor panelists. A dynamic dilution olfactometer was previously designed and built in our lab in accordance with ASTM (American Society for Testing Materials) standard . The instrument has been used by various industries and government agencies for testing odor emissions in the Fraser Valley of BC. It has recently been upgraded to comply with the current international standard which originated from the European initiative (Committé Européen de Normalisation 2003). Further upgrading is taking place with emphasis on odor panelist screening and training to ensure that the strict requirements on the accuracy and reliability of odor analysis are met. Accurate odor emission measurements and subsequent dispersion modeling would enable the best management practices to be devised using integrated preventive and control measures for different agricultural and industrial operations.
Our research on odor control has been focused on the biofiltration technology as applied to composting, pulp mill and farm odors in recent years. A novel biofilter system, which could remove higher levels of air pollutants with a smaller footprint with the help of baffles and flow visualization, was developed from a series of experimental studies. A pilot-scale demonstration project was also conducted on a poultry farm in the Fraser Valley, whereby biofilter, ozonation and fabric filter systems were evaluated for their cost-effectiveness in dust and odor control.
Anaerobic Fermentation for Bioenergy Production
In comparison with conventional methods of producing hydrogen from fossil fuels, biological means of producing hydrogen gas as a clean energy carrier would require less energy inputs and could be considered more sustainable in terms of greenhouse gas emissions. However, the main problem lies with the low hydrogen productivity or yield.
My research work on this subject focuses on the feasibility of generating and enhancing biohydrogen yield from agricultural and food wastes, which are potential important sources of pentose and hexose sugars as carbohydrate substrate. These include manure, food processing waste, wheat straw and cornstalks. The objectives are: 1) to determine the best pre-treatment techniques which can inhibit methane forming bacteria; 2) to control the engineering design parameters or environmental factors in order to establish their optimal values in combination, with an aim to select for hydrogen-producing microorganisms and hence achieve process optimization; 3) to overcome the barriers of the continuous fermentation process and achieve high cell densities and substrate utilization rates via, for instance, using upflow anaerobic sludge blanket type reactors where the microorganisms may be immobilized on the granular bed, and 4) to use membrane technology for minimizing the accumulation of inhibitory metabolic products and purifying the biogas. A related objective is to compare the net energy generation using mesophilic versus thermophilic temperature regimes during the anaerobic fermentation process. The research project would potentially be extended to study the utilization of the biohydrogen produced in an appropriate type of fuel cell, as modular/stationary power source.
Another research project concerns the development of a worksheet-based calculator for anaerobic fermentation of agri-food wastes, and comprises of technology options and engineering economics as the main components. The anticipated software product would allow for the evaluation of emerging technologies aside from well-established ones. The goal is to recommend a viable anaerobic fermentation system for bioenergy production and use in British Columbia. This project is jointly studied with Dr. Sue Baldwin.