Anaerobic reactors

Methane has also been used in aerobic bioreactors that are part of a pump-and-treat operation, and toluene and phenol have also been used as co-substrates at the pilot scale (29). Anaerobic reactors have also been developed for treating trichloroethylene. Eor example, Wu and co-workers (30) have developed a successful upflow anaerobic methanogenic bioreactor that converts trichloroethylene and several other halogenated compounds to ethylene. 

Anaerobic reactor A bioreactor in which no dissolved oxygen or nitrate is present and microbial activity is due to anaerobic bacteria. 

Although some of the examples used for illustration in Chapter 14 impinge on biological wastewater treatment technology, a systematic acconnt of these lies beyond the scope of this volume and the competence of the anthors. It is worth noting, however, that anaerobic reactors that are developed to treat wastewater with the object of producing methane may... 

Zoutberg, G.R. and Frankin, R., Anaerobic treatment of chemical and brewery waste water with a new type of anaerobic reactor the Biobed EGSB reactor, Water Sci. Technol., 34, 375-381, 1996. 

This process, according to the manufacturer,54 has been developed in such a way that space requirements are kept to a minimum. A BIOPAQ IC reactor is used as the initial step in the treatment process. The name of this anaerobic reactor is derived from the gas-lift driven internal circulation that is generated within a tall, cylindrical vessel. These reactors have been operational in the paper industry since 1996. The second step in the purification process is a mechanically mixed and aerated tank. The aerating injectors can be cleaned in a simple way without the need to empty the aeration tank. Potential scaling materials are combined into removable fine particles. At the same time, the materials that may cause an odor nuisance are oxidized into odorless components. The process can be completed by a third and a fourth step. The third step focuses on suspended solids recovery and removal. The fourth step is an additional water-softening step with lamella separation and continuous sand filters in order to produce fresh water substitute. The benefits claimed by the manufacturer are as follows54 ... 

The fate of hormones during sludge treatment has been also poorly documented. Two surveys based on full-scale anaerobic reactors treating sludge concluded that hormones were poorly eliminated or not at all in methanogenic conditions [85, 111]. These results are in accordance with laboratory experiments performed in... 

In order to determine more precisely the fate of pharmaceuticals during sludge treatment, different experiments have been conducted in controlled conditions. In continuous anaerobic reactors treating sludge spiked with pharmaceuticals, Carballa et al. [114] observed removals higher than 80% for naproxen, sulfamethoxazole, and roxithromycin, while 40% and 23% of ibuprofen and iopromide, respectively, were eliminated at both mesophilic (37°C) and thermophilic (55°C) temperatures. For diclofenac and diazepam, elimination of about 60% was observed in mesophilic conditions while in thermophilic conditions, 38% and 73% of these two compounds, respectively, were eliminated. In these experiments, the sludge retention time (15 or 30 days) did not seem to influence pharmaceutical removal... 

Maas R, Chaudhari S (2005) Adsorption and biological decolourization of azo dye Reactive Red 2 in semicontinuous anaerobic reactors. Process Biochem 40 699-705... 

Anaerobic reactor types 1, up-flow anaerobic sludge bed 2, anaerobic fluidized bed 3, anaerobic filter 4, anaerobic rotating disc 5, inclined tubular digester (6, pre-acidification tank)... 

Rai HS, Singh PPS, Cheema TK et al (2007) Decolorization of triphenylmethane dye-bath effluent in an integrated two-stage anaerobic reactor. J Environ Manage 83 290-297... 

Fig. 3.95. Chromatogram of H-acid in the ultrafiltration permeate from the anaerobic reactor injection volume 20 /A, retention time 9.39 min, concentration 0.02 g/1 original, 0.25 g/1 after 11 h biomass treatment. Reprinted with permission from A. Rehorek et al. [155].

The significance of this research showed that they could obtain excellent COD, BOD, TSS and NH3 removals in the effluent of their system with hydraulic residence times between 0.6 and 5 days and they obtained COD/N/P ratios of 167/3.3/1 and 127/2.8/1 which is substantially higher than the Metcalf and Eddy recommended 600 5 1 ratios for anaerobic reactors. Their work was performed at around 35oC + 2Co and their overall reactor treatment train looked like the following Figure 5. 

Both digester systems exhibit extremely low levels of detectable cellulase activities (exoglucanase, endoglucanase, and -glucosidase) when compared to industrial saccharifying processes (See Table III) in which the hydrolysis of cellulose in the feedstock is optimized with respect to enzyme loading. Therefore, the data indicate the level of improvement that may be made to attain maximum rates for cellulose hydrolysis in the anaerobic reactor system. 

Young, J.C. Dhab, M.F. The effect of media design on the performance of fixed bed anaerobic reactors. Water Sci. Technol. 1983, 15, 369. 

Anaerobic reactor configurations that have found application in the treatment of pulp and paper mill effluent include anaerobic contact, UASB, anaerobic filter, UASB/AF hybrid, and fluidized bed reactors. Specific features of these reactors are described in the following sections. 

Thermophilic Anaerobic Reactor Applications. Pulp and paper industries typically discharge warm (50°C) effluents, and conventional reactors operating under mesophilic conditions require cooling of such wastewaters. Attempts have been made periodically by various groups to investigate the possibility of applying thermophilic anaerobic processes to pulp and paper discharges, but to date there is no conclusive evidence to prove the superior performances of thermophilic reactors as compared to their mesophilic counterparts. 

Anaerobic bioreactors have been used since the 1880s to treat wastewaters with large amounts of suspended solids. However, anaerobic reactors are sensitive to toxic pollutants and vulnerable to process upsets, and have been used mainly for municipal sludge digestion. For methane production the sequential metabolism of the anaerobic consortia must be balanced, and the methanogens in particular are vulnerable to process upsets. Recently, anaerobic-aerobic processes (Figure 1.1) have been developed for the mineralization of xenobiotics. These processes take advantage of an anaerobic reactor for the initial reductive dechlorination of polychlorinated compounds or the reduction of nitro substituents to amino substituents. If the reduced compounds are more readily mineralized in an aerobic reactor, an anaerobic-aerobic process is feasible. 

Gavala, H. N., Skiadas, I. V., and Ahring, B. K. 2006. Biological hydrogen production in suspended and attached growth anaerobic reactor systems. Int. J. Hydrogen Energy, 31,1164-1175. 

Yu, H., Zhu, Z., Hu, W., and Zhang, H. 2002. Hydrogen production from rice winery wastewater in an upflow anaerobic reactor by using mixed anaerobic cultures. Int. J. Hydrogen Energy, 27,1359-1365. 

PREDICTING METHANE PRODUCTION FROM AN ANAEROBIC REACTOR 16.29... 

An anaerobic reactor, operated at 35°C, processes a wastewater stream with a flow of 3000 m3/d and a bsCOD concentration of 5000 g/m3. At 95 percent bsCOD removal and a net biomass synthesis yield of 0.04 g VSS/g COD used, what is the amount of methane produced in m3/d ... 

Biodegradation aqueous aerobic L, = 24-168 h, based on unacclimated aqueous screening test data (Dore et al. 1975 Sasaki 1978 selected, Howard etal. 1991) aqueous anaerobic t,/, = 672-4320 h, based on unacclimated anaerobic reactor test data (Chou et al. 1979 selected, Howard et al. 1991)... 

Reactions occur in a continuous flow stirred anaerobic reactor without recycle and operating under steady-state conditions. 

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