Anthony Lau

Biofiltration: A promising and cost‐effective control technology for Odors, VOCs and air toxics

Abstract Biofiltration, a relatively recent air pollution control technology, has been identified as a promising method of odor, VOC and air toxic removal form waste‐gas streams because of low capital and operating costs, low energy requirements and an absence of residual products requiring further treatment or disposal. Biofiltration units are microbial systems incorporating microorganisms grown on a porous solid media like compost, peat, soil or mixture of these materials. The filter media and the microbial culture are surrounded by a thin film of water called biofilm. Waste‐gases containing biodegradable VOCs and inorganic air toxics are vented through this biologically active material, where soluble contaminants partition into the liquid film and are biodegraded by the resident microorganisms in the biofilm. The technology has been successfully applied to a wide range of industrial and public sector sources for the abatement of odors, VOCs and air toxics, with an elimination efficiency of more than 90...

Composting of fish wastes in a full-scale invessel system

Abstract This study carried out in a full-scale fish waste composting facility examined the effects on the ‘active’ stage of composting of two bulking agents (alder and fir), and two amendments (peat moss and vermiculite). The rise in temperature which occurred as composting progressed was accompanied by an increase in ammonia and volatile fatty acid production. This overall pattern was observed in all four mixes, whereby the concentrations of ammonia and volatile fatty acids increased rapidly and then declined gradually over the course of monitoring. The changes in their concentrations over time proved to be a reliable indicator of the progress of the composting process. Ammonia emissions from the composting piles were reduced by the additions of peat moss, vermiculite, and alder, in comparison to the headspace ammonia level for the fir mix. The results indicated that ammonia management during the composting process could be easily accomplished by the use of suitable amendments or bulking agents. Peat moss and vermiculite were found to be good amendments for fish composting and alder was found to be a good bulking agent.

Aeration experiments for swine waste composting

Abstract A study was undertaken to investigate aeration in the composting of swine manure. Three sets of aeration experiments were conducted to determine the optimum aeration rate. Both continuous and intermittent modes of aeration were tested. Temperature was monitored as the most important indicator of the efficiency and effectiveness of the composting process. Physical and chemical characteristics (moisture content, percent weight loss, total nitrogen, C:N ratio and pH) of compost were also determined. In all experiments except for continuous aeration with rates of 1·0 and 2·0 l/min kg volatile matter, a temperature of 55°C was reached within 2 days and remained above this level for 4–7 days, thus satisfying the regulatory requirements for a PFRP (Process to Further Reduce Pathogens). The results indicated that the temperature of the compost pile was controlled by the aeration rate in combination with the frequency and the duration of aeration. It is recommended that an aeration rate of 0·04–0·08 l/min kg volatile matter and an intermittent mode of aeration should be adopted for swine manure composting.

Biofiltration control of pulping odors - hydrogen sulfide : Performance, macrokinetics and coexistence effects of organo-sulfur species

The work reported here describes the aerobic biodegradation of reduced sulfur compound mixtures in air streams by biofilters. Rates of removal of hydrogen sulfide as a sole substrate and in the presence of organo-sulfur compounds were determined to see if there were any inhibitory effects of the organo-sulfur compounds on the rate of hydrogen sulfide removal. Experiments were conducted in three bench-scale biofilters packed with the mixtures of compost/perlite (4:1), hog fuel/ perlite (4:1), and compost/hog fuel/perlite (2:2:1), respectively. Hydrogen sulfide, the predominant odorous gas produced from kraft pulping processes, was used as the main pollutant (substrate). Other organo-sulfur species (dimethyl sulfide and dimethyl disulfide), also emitted from kraft pulp mills, were used as competing (secondary) substrates in the waste gas stream. To describe rates of removal a Michaelis–Menten type kinetic equation was modified to incorporate the plug flow behavior of biofilters, and used in evaluating the pseudo-kinetic parameters, Vmax (the maximum removal rate) and Km (the half saturation concentration), for hydrogen sulfide biodegradation, and the type of macrokinetic competition between hydrogen sulfide and the organo-sulfur compounds. No significant differences in V max for the three biofilters were observed. The V max ranged between 136 and 147 g m−3 h −1, while the Km varied from 44 to 59 ppmv for the three biofilters. Hydrogen sulfide elimination capacity was not affected by the presence of any of the organo-sulfur species in all of the three biofilters, confirming earlier results that hydrogen sulfide removal in biofilters is independent of the presence of organo-sulfur compounds mainly because of its easy biodegradability. © 1999 Society of Chemical Industry

Quality of Wood Pellets Produced in British Columbia for Export

Wood pellet production and its use for heat and power production are increasing worldwide. The quality of export pellets has to consistently meet certain specifications as stipulated by the larger buyers, such as power utilities or as specified by the standards used for the non-industrial bag market. No specific data is available regarding the quality of export pellets to Europe. To develop a set of baseline data, wood pellets were sampled at an export terminal in Vancouver, British Columbia, Canada. The sampling period was 18 months in 2007-2008 when pellets were transferred from storage bins to the ocean vessels. The sampling frequency was once every 1.5 to 2 months for a total of 9 loading/shipping events. The physical properties of the wood pellets measured were moisture content in the range of 3.5% to 6.5%, bulk density from 728 to 808 kg/m3, durability from 97% to 99%, fines content from 0.03% to 0.87%, calorific value as is from 17 to almost 18 MJ/kg, and ash content from 0.26% to 0.93%.The diameter and length were in the range of 6.4 to 6.5 mm and 14.0 to 19.0 mm, respectively. All of these values met the published non-industrial European grades (CEN) and the grades specified by the Pellet Fuel Institute for the United States for the bag market. The measured values for wood pellet properties were consistent except the ash content values decreased over the test period.

Effects of key operational parameters on biohydrogen production via anaerobic fermentation in a sequencing batch reactor

In this study, a series of tests were conducted in a 6L anaerobic sequencing batch reactor (ASBR) to investigate the effect of pH, hydraulic retention time (HRT) and organic loading rate on biohydrogen production at 28°C. Sucrose was used as the main substrate to mimic carbohydrate-rich wastewater and inoculum was prepared from anaerobic digested sludge without pretreatment. The reactor was operated initially with nitrogen sparging to form anaerobic condition. Results showed that methanogens were effectively suppressed. The optimum pH value would vary depending on the HRT. Maximum hydrogen production rate and yield of 3.04 L H(2)/L reactor d and 2.16 mol H(2)/mol hexose respectively were achieved at pH 4.5, HRT 30 h, and OLR 11.0 kg/m(3)d. Two relationships involving the propionic acid/acetic acid ratio and ethanol/acetic acid ratio were derived from the analysis of the metabolites of fermentation. Ethanol/acetic acid ratio of 1.25 was found to be a threshold value for higher hydrogen production.

Odor Measurements for Manure Spreading Using a Subsurface Deposition Applicator

Odor emissions during manure spreading events have become a source of concern, particularly where farms are located nearby urban areas. The objective of the present study was to compare odor concentrations and odor emission rates due to pig manure application using two different types of applicators, a sub‐surface deposition system and a conventional splash‐plate applicator. Air samples were collected using a Surface Isolation Flux Chamber and the “bag‐in‐vacuum chamber” techniques, at 0.5, 1.5 and 2.5 hours after manure application. A three‐station forced‐choice dynamic dilution olfactometer was used by an odor panel for determining odor concentration. Preliminary results indicated that with the sub‐surface deposition system applicator odor emission rate was reduced by 8% to 38% compared to that of the conventional splash‐plate applicator. The highest reduction in odor strength and odor emission rate was observed in the most offensive period after manure application. The sub‐surface deposition system may be a solution for hog producers who wish to reduce odor complaints from applying manure without the cost and problems associated with deep injection systems.

SO2-catalyzed steam pretreatment enhances the strength and stability of softwood pellets

Densification can partially resolve the logistical challenges encountered when large volumes of biomass are required for bioconversion processes to benefit from economies-of-scale. Despite the higher bulk density of pellets, their lower mechanical strength and sensitivity to moisture are still recurring issues hindering long term transportation and storage. In this study, we have evaluated the potential benefits of SO(2)-catalyzed steam treatment to achieve both the needed size reduction prior to pelletization while improving the stability of the produced pellets. This pretreatment substantially reduced the particle size of the woodchips eliminating any further grinding. The treated pellets had a higher density and exhibited a two-time higher mechanical strength compared to untreated pellets. Despite a higher moisture adsorption capacity, treated pellets remained intact even under highly humid conditions. The high heating values, low ash content and good overall carbohydrate recovery of treated pellets indicated their potential suitability for both biochemical and thermochemical applications.

Evaluation of swine waste composting in vertical reactors

Abstract This study examined the composting of swine wastes in a modified static pile system. Variations in the heights of the reactors and differences in the initial moisture contents of the compost mix were the variables under consideration. The effectiveness of the process was assessed on the basis of the physical parameters of temperature, moisture content, particle size distribution, shrinkage and compaction. The reactor with a compost pile height of 1.0 m had the best results with both initial moisture contents. However, the results for all the reactors improved when the initial moisture content was lower. This suggests that although the reactor with a pile height of 2.3 m gave the least favourable results, control of aeration and initial moisture levels could make this height of composting pile effective.

Effect of Steam Treatment on Pellet Strength and the Energy Input in Pelleting of Softwood Particles

Three whitewood species (spruce, Douglas fir, and pine) and one sample of bark (Douglas fir) were treated with high-pressure steam at 220°C for 5 min. The steam treatment resulted in a reduction in average particle size by as much as 25%. Pine particles showed the largest reduction in size, while bark showed the least. Despite a slightly lower density, pellets made from treated particles had a higher mechanical strength (hardness) than untreated pellets. The mechanical energy required to compact steam-treated material was higher than the energy required to make pellets from untreated wood. Douglas fir required the least energy input among debarked samples. Spruce was the stickiest pellet to be pushed out of the cylindrical die. Bark pellets required the lowest energy to be compacted and pushed out of the cylindrical die. The overall conclusion is that steam treatment reduces particle size, reduces pellet density slightly, but increases the mechanical strength of the produced pellets. Steam treatment increases the energy input required to make pellets, and more energy is required to push pellets out of the die compared to pellets made from untreated biomass.