Empirical modelling and dual-performance optimisation of a hydrogen sulphide removal process for biogas treatment.

This study was conducted in order to investigate the use of a simple, low-cost technology for the removal of hydrogen sulphide (H(2)S) from biogas, consisting of an anoxic biotrickling filter. Modelling and optimisation of the process was achieved by studying two independent variables (H(2)S concentration and biogas flowrate) and two simultaneous performance criteria (H(2)S removal efficiency (%) and H(2)S loading rate (g/(m(3) bed day)), which were inversely related. The experiments were carried out on a bioreactor with a 12 L packing volume. H(2)S concentration and biogas flowrate were varied in the range of 2000-4000 ppm(v) and 10-70 L/h, respectively. A model sensitivity analysis indicated the influence of the process variables on the bioreactor performance. Process optimisation was undertaken on a H(2)S removal efficiency basis, while maintaining a target H(2)S loading rate, depending on the desired quality for the biogas use and the technological requirements.

Evaluation of different packing media for anoxic H2S control in biogas.

This paper presents the experimental results obtained during the operation of two biotrickling filters packed with 6.7 L of commercially available plastic fibres and lava rocks, respectively. The biotrickling filters were tested under similar operating conditions for hydrogen sulphide (H2S) removal from biogas under anoxic conditions, in order to determine the influence of biogas flow rate and H2S concentration on the process performance and to facilitate process modelling. The biogas flow rate was adjusted to between 25 and 75 L/h, while the input H2S concentration was varied between 500 and 1500 ppmv. The process performance was evaluated by two simultaneous system responses, namely the H2S removal efficiency and H2S loading rate, which were subsequently described by a second-order empirical model and an interaction model, respectively. Good agreement between the experimental results, model prediction and simultaneous dual-response simulation was obtained.

Buffer requirements for enhanced hydrogen production in acidogenic digestion of food wastes.

The requirements for pH buffer addition for hydrogen production and acidogenesis in batch acidogenic digestion of a food waste (FW) feedstock with limited alkalinity was studied at various initial pH conditions (6.0-8.0). The results showed that, without buffer addition, hydrogen production from this feedstock was insignificant regardless of the initial pH. With buffer addition, hydrogen production improved significantly if the initial pH was greater than 6.0. Substantial hydrogen production occurred when the pH at the end of the batch digestion was higher than 5.5. The maximum hydrogen production was found to be 120 mL/g VS added when the initial pH was 6.5 and buffer addition was in the range of 15-20 mmol/g VS. The effect of pH buffering on the formation of volatile fatty acids (acetic acid, propionic acid and butyric acid) was similar to its effect on hydrogen production. The results of this study clearly indicated shifts in the metabolic pathways with the pH of fermentation. The changes in metabolic pathways impacted upon the dosage of buffer that was required to achieve maximum hydrogen generation.

Co-production of hydrogen and methane from potato waste using a two-stage anaerobic digestion process.

Hydrogen and methane co-production from potato waste was examined using a two-stage process of anaerobic digestion. The hydrogen stage was operated in continuous flow under a pH of 5.5 and a HRT of 6h. The methane stage was operated in both continuous and semi-continuous flows under HRTs of 30 h and 90 h, respectively, with pH controlled at 7. A maximum gas production rate of 270 ml/h and an average of 119 ml/h were obtained from the hydrogen stage during the operation over 110 days. The hydrogen concentration contained in the gas was 45% (v/v), on average. The maximum and average gas production rates observed from methane reactor during the 74 days of semi-continuous flow operation were 187 and 141 ml/h, respectively, with an average methane concentration of 76%. Overall, 70% of VS, 64% of total COD in the feedstock were removed. The hydrogen and methane yields from the potato waste were 30 l/kg TS (with a maximum of 68 l/kg) and 183 l/kg TS (with a maximum of 225 l/kg), respectively. The total energy yield obtained was 2.14 kW h/kg TS, with a maximum of 2.74 kW h/kg TS.

Potential for hydrogen and methane production from biomass residues in Canada.

Canada generates approximately 1.45 x 10(8)t of residual biomass per year, containing an estimated energy value of 2.28 x 10(9)GJ, which is equivalent to about 22% of Canada's current annual energy use. Anaerobic digestion of these biomass residues using conventional technologies could generate 1.14 x 10(10)m(3)/year of CH(4) with a heating value of 4.56 x 10(8)GJ. Conversion of these residues using emerging technologies that favor the synthesis of H(2) and represses the synthesis of CH(4) could generate 1.47 x 10(10)m(3)/year renewable H(2), with a heating value of 1.89 x 10(8)GJ. While CH(4)-production results in a larger amount of energy recovery, generating H(2) from waste biomass is a renewable alternative that could fuel the hydrogen economy. Additional research to further both the technical and commercial development of microbial bio-energy from biomass is warranted.

Occurrence and reductions of pharmaceuticals and personal care products and estrogens by municipal wastewater treatment plants in Ontario, Canada.

Over the last ten years there have been reports of pharmaceuticals and personal care product (PPCP) residuals in municipal wastewater treatment plant (WWTP) effluents. The principle goal of this study was specifically to expand and in some cases establish a Canadian database for the presence of selected acidic drugs, triclosan, polycyclic musks, and selected estrogens in MWWTP influent and effluent. The impact of treatment configuration (e.g. lagoons, conventional activated sludge (CAS), and CAS followed by media filtration (CAS+filtration)) was also examined. For CAS systems, the most prevalent treatment type, the effect of operating temperature and SRT was evaluated. Selected PPCPs included ten acidic pharmaceuticals (i.e. a group of pharmaceuticals that are extractable at a pH of 2 or less), triclosan, five polycyclic musks and two estrogens. The pharmaceuticals and musks were selected on the basis of levels of use in Canada; reported aquatic toxicity effects; and the ability to analyze for the compounds at low levels. Twelve MWWTPs discharging into the Thames River, the second largest river in southwestern Ontario, were surveyed. The only common characteristic of acidic drugs is their extraction pH as they differ in their intended biological function and chemical structure. Many organics degraded by WWTP processes benefit from warm temperatures and long SRTs so the impact of these variables warranted additional attention. Influent concentrations and reductions for acidic drugs reported by this study were compared to other Canadian studies, when available, and European investigations. The data of this study seems consistent with other reports. Ten acidic drugs were considered by this study. Three were consistently present at non-quantifiable levels (e.g. CLF, FNP and FNF). Additionally, one analyte, SYL, presented results that were so inconsistent that the values were not analysed. The remaining six acidic pharmaceuticals were placed into three categories. IBU and NPX members of the first category had consistently high reductions. At the level of reduction achieved (i.e. median reduction of greater than 93%) and any effect of treatment type or operating characteristics would be subtle and non-discernable given the analytical noise. In the second group are KTP and IND, and definitive comments are difficult to make on the impact of treatment type and operational considerations due to a sparse data set (i.e. many influent values were at non-quantifiable concentrations). Median reductions were in the 23% to 44% range. In the last category are GMF and DCF which have median reductions of 66% and -34%, respectively. Several negative reduction values in the data set (i.e. twelve of twenty six sampling events) suggest that DCF may be deconjugated under certain conditions. This warrants further evaluation when analytical methods for measuring human metabolites of DCF are available. For both GMF and DCF, reduction does not appear to be strongly influenced by SRTs up to 15 days, while SRTs over 30 days were associated with more frequent non-quantifiable effluent levels of DCF. This would suggest that better treatment would be provided by lagoons and CAS systems with extended aeration. Preliminary data suggests that temperature does not play a strong role in the reduction of these compounds. Triclosan (TCL) was detected at concentrations of 0.01-4.01 microg/L in influent samples and 0.01-0.324 microg/L in effluent samples. Reduction of TCL ranged from 74% to 98%. Lagoon treatment seems to be the best TCL reduction as it was present in the influent and effluent at quantifiable and non-quantifiable concentrations, respectively, on nine of nine sampling occasions. Influent and reduction values of five polycyclic musks (e.g. ADBI, AHMI, ATII, HHCB, and AHTN) were examined over the course of this study. AHMI was predominantly present at non-quantifiable concentrations. HHCB and AHTN were present at the highest concentrations. A comparison between Canadian values and those of European studies indicate that in general polycyclic musk concentrations in Canadian MWWTP effluents are 5-10 times lower. More extensive European and Canadian databases would be useful in confirming this initial observation. Median reductions for the five remaining musks range between 37% and 65% in CAS systems. CAS+filtration systems would be expected to have higher reductions if musks were bound to the effluent solids. This trend is not apparent but this may be due to the small size of the data set. In lagoon systems, musk reduction for HHCB and AHTN are approximately 98-99%. For ADBI and ATII musk, there are no numerical reduction values as most often the effluent concentration was non-quantifiable. In some instances, both the influent and effluent concentrations were non-quantifiable. The hormones 17-beta-estradiol (E2) and estrone (E1) were detected at concentrations of 0.006 to 0.014 and 0.016 to 0.049 microg/L, respectively. E2 was not detected in any effluent samples (<0.005 microg/L) whereas E1 was detected in effluent samples from CAS treatment plants (median of 0.008 microg/L), and in one sample from lagoons. These data demonstrate that there are detectable levels of PPCPs entering Canadian waterways at trace levels, and that only some of these compounds are being reduced in a significant proportion by municipal wastewater treatment processes.