Huub H. J. Cox

Anaerobic codigestion of municipal, farm, and industrial organic wastes : A survey of recent literature

Codigestion of organic wastes is a technology that is increasingly being applied for simultaneous treatment of several solid and liquid organic wastes. The main advantages of this technology are improved methane yield because of the supply of additional nutrients from the codigestates and more efficient use of equipment and cost-sharing by processing multiple waste streams in a single facility. Many municipal wastewater treatment plants (WWTPs) in industrialized countries currently process wastewater sludge in large digesters. Codigestion of organic wastes with municipal wastewater sludge can increase digester gas production and provide savings in the overall energy costs of plant operations. Methane recovery also helps to reduce the emission of greenhouse gases to the atmosphere. The goal of this literature survey was to summarize the research conducted in the last four years on anaerobic codigestion to identify applications of codigestion at WWTPs. Because the solids content in municipal wastewater sludge is low, this survey only focuses on codigestion processes operated at relative low solids content (slurry mode). Semi-solid or solid codigestion processes were not included. Municipal wastewater sludge, the organic fraction of municipal solid waste, and cattle manure (CAM) are the main wastes most often used in codigestion processes. Wastes that are codigested with these main wastes are wood wastes, industrial organic wastes, and farm wastes. These are referred to in this survey as codigestates. The literature provides many laboratory studies (batch assays and bench-scale digesters) that assess the digestibility of codigestates and evaluate the performance and monitoring of codigestion, inhibition of digestion by codigestates, the design of the process (e.g., single-stage or two-stage processes), and the operation temperature (e.g., mesophilic or thermophilic). Only a few reports on pilot- and full-scale studies were found. These evaluate general process performance and pretreatment of codigestates, energy production, and treatment costs.

Biological waste air treatment in biotrickling filters

Recent studies in the area of biological waste air treatment in biotrickling filters have addressed fundamental key issues, such as biofilm architecture, microbiology of the process culture and means to control accumulation of biomass. The results from these studies have provided a deeper insight into the fundamental mechanisms involved during biotrickling filtration. In the coming years, these and future advances should allow for the design of better reactor controls and the improvement of pollutant removal in these gas phase bioreactors. Ultimately, this should lead to a more widespread use of biotrickling filters for air pollution control.

Biomass control in waste air biotrickling filters by protozoan predation.

Two protozoan species as well as an uncharacterized protozoan consortium were added to a toluene-degrading biotrickling filter to investigate protozoan predation as a means of biomass control. Wet biomass formation in 23.6-L reactors over a 77-day period was reduced from 13.875 kg in a control biotrickling filter to 11.795 kg in a biotrickling filter enriched with protozoa. The average toluene vapor elimination capacity at 1 g/m3 toluene and 64 m3/(m3. h) was 31.1 g/(m3. h) in the control and 32.2 g/(m3. h) in the biotrickling filter enriched with protozoa. At higher toluene inlet concentrations, toluene degradation rates increased and were slightly higher in the biotrickling filter enriched with protozoa. The lower rate of biomass accumulation after the addition of protozoa was due to an increase of carbon mineralization (68% as compared to 61% in the control). Apparent biomass yield coefficients in the control and enriched trickling filter were 0.72 and 0.59 g dry biomass/g toluene, respectively. The results show that protozoan predation may be a useful tool to control biomass in biotrickling filters, however, further stimulation of predation of the biomass immobilized in the reactor is required to ensure long-term stability of biotrickling filters.

CHEMICAL REMOVAL OF BIOMASS FROM WASTE AIR BIOTRICKLING FILTERS: SCREENING OF CHEMICALS OF POTENTIAL INTEREST

A protocol was developed to rapidly assess the eAciency of chemical washing for the removal of excess biomass from biotrickling filters for waste air treatment. Although the experiment was performed on a small scale, conditions were chosen to simulate application in full-scale biotrickling filters. From 18 treatments with diAerent combinations and concentrations of chemicals, only washing with 0.4% (w/v) NaOH, 0.26 and 1.31% (w/v) NaClO and 11.3% (w/v) H2O2 resulted in a biomass removal significantly higher than treatment with pure water with wet biomass removal eAciencies of 50.2, 49.2, 77.0 and 69.0%, respectively. Biomass removal by H2O2 and NaClO was accompanied by complete loss of activity of unremoved biomass, whereas after treatment with NaOH low residual bio- logical activity was observed. However, treatment with NaOH resulted in generation of relatively large amounts of suspended solids (22.3% of dry biomass removed) and dissolved carbon (65.3% of C-bio- mass removed). NaClO was found to be the most promising reagent for biomass control in biotrickling filters because of its ability to remove large amounts of biomass and its low cost. # 1999 Elsevier Science Ltd. All rights reserved

Enrichment of fungi and degradation of styrene in biofilters

SummaryExperiments were set up in order to enrich styrene-degrading fungi in biofilters under conditions representative for industrial off-gas treatment. From the support materials tested, polyurethane and perlite proved to be most suitable for enrichment of styrene-degrading fungi. The biofilter with perlite completely degraded styrene when amounts ranging between 290 and 675 mg/m in the influent gas were present. An elimination capacity of at least 70 g styrene per m3 filter bed per hour was calculated.

Influence of the water content and water activity on styrene degradation by Exophiala jeanselmei in biofilters

Abstract The performance at low water availability of styrene-degrading biofilters with the fungus Exophiala jeanselmei growing on perlite, the inert support, was investigated. E. jeanselmei degrades styrene at a water activity of 0.91–1. In biofilters, the styrene elimination capacity at a water activity of 0.91 is 5% of the maximal elimination capacity of 79 g m-3 h-1 (water activity 1). Application of dry air results in a rapid loss of styrene degradation activity, even at 40%–60% (w/w) water in the filter bed and at a water activity of 1. Humidification of the gas and an additional supply of water to the filter bed are necessary to maintain a high and stable styrene elimination capacity.

Growth of the black yeast Exophiala jeanselmei on styrene and styrene-related compounds

The black yeast Exophiala jeanselmei can grow on styrene as the sole source of carbon and energy in concentrations up to 0.36 mm. No growth is observed at higher styrene concentrations. Styrene oxidation is induced by styrene or styrene-related compounds, whereas glucose represses this styrene oxidation. E. jeanselmei shows a broad substrate specificity: various aromatic compounds are used as the sole source of carbon and energy. Styrene-grown cells can oxidize styrene, styrene oxide, phenylacetaldehyde, phenylacetic acid and 2-phenylethanol at a rate of 1.3 to 3.2 μg O2·min−1·mg−1 protein. A pathway for the degradation of styrene in E. jeanselmei is suggested.

Toluene degradation in the recycle liquid of biotrickling filters for air pollution control

Abstract Pollutant degradation in biotrickling filters for waste air treatment is generally thought to occur only in the biofilm. In two experiments with toluene degrading biotrickling filters, we show that suspended microorganisms in the recycle liquid may substantially contribute to the overall pollutant removal. Two days after reactor start up, the overall toluene elimination capacity reached a maximum of 125 g m−3 h−1, which was twice that found during prolonged operation. High biodegradation activity in the recycle liquid fully accounted for this short-term peak of pollutant elimination. During steady-state operation, the toluene degradation in the recycle liquid was 21% of the overall elimination capacity, although the amount of suspended biomass was only 1% of the amount of immobilized biomass. The results suggest that biotrickling filter performance may be improved by selecting operating conditions allowing for the development of an actively growing suspended culture.

INNOVATIVE EXPERIMENTAL SETUP FOR THE PARALLEL OPERATION OF MULTIPLE BENCH SCALE BIOTRICKLING FILTERS FOR WASTE AIR TREATMENT

A new concept of periodically rotating biotrickling filters was developed for parallel operation of multiple bench scale biotrickling filters without the requirement for expensive equipment such as liquid recycle pumps and air flow regulation. The performance of 20 identically operated rotating biotrickling filters was reproducible with an average toluene elimination capacity of 79.4 g m−3 h−1 (s.d. = 5.7) at an empty bed residence time of 45 s and a toluene inlet gas phase concentration of 1.6 g m−3. At gas and liquid cocurrent operation, the toluene elimination capacity of rotating biotrickling filters was 20% higher than at countercurrent operation. This was probably caused by greater mass transfer limitation resulting from increased wetting of the biofilm during countercurrent operation. Performance versus load curves of rotating and of conventional biotrickling filters were comparable with non-zero order removal at toluene inlet concentrations lower than 2 g m−3. This multiple rotating biotrickling filters setup provides a new and inexpensive tool for comparative studies in biotrickling filtration for air pollution control.

Application of Styrene-Dregrading Fungi in Biofilters

As a consequence of the Dutch “Hydrocarbon 2000” Programma, the industry will have to reduce the emission of styrene. Biological degradation in biofilters may offer an economically feasible method for the purification of low concentration (< 1 g/m3) styrene waste gases. However, microbial filters for styrene degradation currently available suffer from instability. Therefore, it is our objective to develop stable biofilters which rely on fungi as the active catalyst for the treatment of styrene-containing waste gases. Compared to bacteria, fungi are generally more tolerant to low water activity and they retain activity at low pH. Application of styrene-degrading fungi in biofilters may offer two advantages: 1. Stringent control of the water activity and/or pH in the filter is less important. 2. Reduction of the water activity may improve the mass transfer of poorly water soluble compounds like styrene.