Downflow Stationary Fixed Film Research Articles

Evaluation of the optimum conditions of an anaerobic Down-flow Stationary Fixed Film reactor for swine wastewater treatment

The Down-flow Stationary Fixed Film (DSFF) reactor is a downstream anaerobic reactor combined with a fixed layer of adhesive media that is capable of handling large organic loads, has cheap investment costs, and has a shorter treatment time than other conventional anaerobic technologies. In this study, the DSFF reactor was used to investigate its potential to remove contaminants from swine wastewater. The optimal operating conditions of the DSFF reactor including hydraulic retention time (HRT), organic concentration, and nutrient ratio were investigated. The obtained results showed that the COD removal efficiency increased from 50% to 79.721% when the influent COD enhanced from 500 to 3000 mg/L. The COD removal efficiency was 85.66%, 61.71% and 50.81% at three different nutritional ratios of C/N/P:250/1.5/1, C/N/P:250/7.5/1, and C/N/P:250/7.5/0.2, respectively. The overall results revealed that the optimal HRT is 12 hours, the optimal COD concentration is between 2000 mg/L and 3000 mg/L, and the optimal nutrient ratio is C/N/P:250/1.5/1. The DSFF reactor effectively manages BOD and phosphorus removal while handling a range of contamination levels in swine wastewater. Furthermore, there is no significant sludge loss and the operation mode is simple. This reactor is potentially appropriate for implementation in pig farming households.

Anaerobic digestion of peel waste and wastewater for on site energy generation in a citrus processing facility

A citrus processing facility produces significant quantities of both peel waste and wastewater. A leach – bed batch anaerobic digester was operated successfully at thermophilic (55 °C) temperature for biogasification of citrus peel waste. The retention time in the digester was 25 days. The citrus processing wastewater was digested in a thermophilic DSFF (down flow stationary fixed film) anaerobic reactor fed continuously and operated for 76 days. At an average organic loading rate of 0.51 kg sCOD m−3 d−1 the hydraulic retention time was 16 days. No long term toxicity issues due to limonene were observed during digestion of both citrus waste feedstocks. Biogasification yielded, 0.116 m3 methane at STP kg−1 peel waste received and 2.1 m3 at STP m−3 wastewater received. An energy analysis showed that in a citrus processing plant handling 600 tons per day of fruits, the biogas produced from the waste streams is more than sufficient to meet all the electricity and fuel demands. Excess electricity generated from biogas may be sold generating estimated revenues of more than a $1 million annually (at electricity sale price of $0.04/kWhe).

Treatment of Sugar Industry Wastewater in Anaerobic Downflow Stationary Fixed Film (DSFF) Reactor

The consumption of large volumes of water and the generation of organic compounds as liquid effluents are major environmental problems in sugar cane processing industry. The aim of this work is to study the treatment of synthetic sugar wastewater by a downflow stationary fixed film (DSFF) reactor. The reactor was fabricated and packed with polyvinyl chloride pipe pieces and it was air tight sealed to maintain anaerobic conditions. The ambient room temperature during the study period was between 29 and 33 °C. Start-up period required by the reactor was 3 weeks. Initially a hydraulic retention time (HRT) of 48 h was set, HRT was decreased when the reactor reached steady state. BOD and COD removal increased as the HRT decreased from 48 to 12 h. BOD and COD removal was 79 and 81.8 % respectively at 12 h HRT. A decline in removal was noticed when the HRT was set to 6 h. Biogas production was 445 ml/day at 12 h HRT. Differential staining was carried out, it revealed that the micro-organisms belong to gram negative class. Thus DSFF reactor can be used for treating sugar wastewater and for producing biogas.

Anaerobic digestion of corn ethanol thin stillage in batch and by high-rate down-flow fixed film reactors

Thin stillage (CTS) from a dry-grind corn ethanol plant was evaluated as a carbon source for anaerobic digestion (AD) by batch and high rate semi-continuous down-flow stationary fixed film (DSFF) reactors. Biochemical methane potential (BMP) assays were carried out with CTS concentrations ranging from approximately 2,460-27,172 mg total chemical oxygen demand (TCOD) per litre, achieved by diluting CTS with clean water or a combination of clean water and treated effluent. High TCOD, SCOD and volatile solids (VS) removal efficiencies of 85 ± 2, 94 ± 0 and 82 ± 1% were achieved for CTS diluted with only clean water at an organic concentration of 21,177 mg TCOD per litre, with a methane yield of 0.30 L methane per gram TCOD(removed) at standard temperature and pressure (STP, 0 °C and 1 atmosphere). Batch studies investigating the use of treated effluent for dilution showed promising results. Continuous studies employed two mesophilic DSFF anaerobic digesters treating thin stillage, operated at hydraulic retention times (HRT) of 20, 14.3, 8.7, 6.3, 5 and 4.2 d. Successful digestion was achieved up to an organic loading rate (OLR) of approximately 7.4 g TCOD L(-1)d(-1) at a 5 d HRT with a yield of 2.05 LCH(4) L(-1)d(-1) (at STP) and TCOD and VS removal efficiencies of 89 ± 3 and 85 ± 3%, respectively.

Performance Analysis of Anaerobic Downflow Stationary Fixed Film (DSFF) Bioreactors and Software Development

The performance of an anaerobic downflow stationary fixed film bioreactor has been simulated mathematically and a software package developed. Each flow channel of the reactor is assumed equivalent to a tubular reactor with a specific degree of axial dispersion. The variation of axial dispersion coefficient along the length of the flow channel (due to the change in gas velocity ) is accounted for and so is resistance to substrate transfer into biofilm which is taken into account by incorporating effectiveness factor into performance equations. Effectiveness factor is computed by numerically integrating the expression for intrinsic rate and the package is applicable to all forms of kinetic equations. Experimental data from pilot plants exhibit encouraging agreement with results predicted by the developed simulation package.

Effects of disintegration on anaerobic degradation of sewage excess sludge in downflow stationary fixed film digesters

The effects of mechanical disintegration on anaerobic digestibility of sewage excess sludge in downflow stationary fixed film (DSFF) digesters were investigated on laboratory scale. Mechanical pretreatment using a high pressure homogenizer led to significantly enhanced concentrations of soluble proteins and carbohydrates in the feed sludge. Using DSFF digesters with two different tubular plastic media as support material it was shown that a stable digestion process could be achieved at hydraulic retention times (HRT) down to 5 days. Compared to conventional digesters at 10 d and 15 d HRT respectively, the degradation of volatile solids was enhanced up to 25%, also resulting in a higher specific biogas production. Further investigations on degradation of soluble proteins and carbohydrates showed that a slowly degradable fraction of carbohydrates was released via disintegration. Using the distribution of chain length and the concentrations of volatile fatty acids as process parameters, the dependability on the HRT and the degree of disintegration (the release of soluble COD) predominated the effects of specific surface area of the support media.

Evaluation of a pilot scale downflow stationary fixed film anaerobic reactor treating piggery slurry in the mesophilic range

Some aspects of the operational studies of a Pilot Scale Downflow Stationary Fix Film Anaerobic Reactor treating sieved piggery slurries (1 mm mesh) are presented. Conditions affecting anaerobic digestion were analyzed. The organic loading rate to the reactor was modified, controlling variation in the recirculation rate and the temperature. The experiments were accomplished in the mesophilic range (35°C). Hydraulic retention time was operated between 6 and 0.9 days with no souring of the system. A medium organic load reduction was achieved, about 60% Total COD and 50% VS, both related to HRT longer than 3 days. Biogas productivity resulted in 4.5 m 3/m 3 d −1 for that HRT. The gas composition displayed a certain uniformity in methane and carbon dioxide content with little variation in nitrogen, traces of hydrogen were found. A decrease in the gas production was observed when reducing the HRT below 2 days, leading to a stabilization around 4.0 m 3/m 3 d −1. The results were adjusted to the Chen and Hashimoto kinetic model, attaining the wash-out HRT, and the value of the kinetic constants. The study at a pilot scale suggests the convenience of the DSFF system for the design of full-scale plants for slurries from piggery farms.

Anaerobic filter and DSFF reactors in anaerobic treatment of tuna processing wastewater

An anaerobic filter (AF) and a downflow stationary fixed film (DSFF) reactor were used for the treatment of a tuna processing wastewater. Start-up of the anaerobic reactors was improved using lactose as co-substrate. The AF removed up to 75% of the influent COD concentrations at organic loading rates (OLR) of 11-13 kg COD m−3 d−1, whereas the DSFF reactor removed 70% at 3 kg COD m−3 d−1. Based on these results it appears that anaerobic treatment systems are applicable to tuna processing industry wastewaters and that the AF shows a much better performance, allowing higher organic loadings and COD removal efficiencies than the DSFF reactor.

Anaerobic purification of brewery wastewater in biofilm reactors with and without a methanation cascade

A laboratory scale anaerobic treatment process for brewery wastewater has been investigated. It utilised a continuously stirred tank (CST) acidification reactor (11.3 1) plus an anaerobic treatment system which consisted of either a downflow stationary fixed film (DSFF) reactor (20.7 1) or a DSFF reactor in series with a floc (FLOC) or sludge blanket reactor (20.8 1). At the same residence time the combination of DSFF and FLOC reactor performed better than a single methane digester. Using low and high strength wastewater, degradation yields of 80-90% were obtained at total loading rates BR,COD up to 10 kg COD m−3 × d and a residence time t less than one day. Mean values of methane yield were 0.31 m3STP kg-1 COD or 2.91 m3STP m−3 × d. Inert support media investigated consisted of inorganic materials such as porous Kerapor 1000 and glass sponge (Siran) with macro- and micropores or polyurethane foam (Filtren TR 30) with an open net structure. In all cases SEM showed appropriate surface characteristics for microbial attachment. After 4 months of operation biofilm thickness on inorganic support media was 0.4-0.9 mm at a superficial linear velocity (SLV) of 10-5 mm min−1. Under these conditions biofilm on Filtren TR 30 was noticeably thicker (up to 2 mm). Concerning metal contamination of biofilm on Filtren TR 30, Al, Fe and Zn showed elevated levels above 2000 ppm.

Anaerobic Wastewater Treatment in Downflow Stationary Fixed Film Reactors

Design features and performance of the downflow stationary fixed film reactor for anaerobic wastewater treatment are reviewed. Media characteristics, feed characteristics and loading rates found to provide rapid start-up and maximum treatment efficiency are discussed. It is concluded that the reactor is a useful research tool for studying anaerobic treatment. The reactor is not as sensitive to waste characteristics as other second generation anaerobic reactors. The reactor is able to handle wastes with high suspended solids content and provide efficient treatment with a minimum clogging potential. DSFF operation is simple and stable; however, loading rates attainable in this reactor are not as high as those attained with other processes due to lower biomass retention capacity.

Treatment of Distillery Wastewater Using an Anaerobic Downflow Stationary Fixed-Film Reactor: Performance of a Large Plant in Operation for Four Years

The results of the first four years' operation of a downflow submerged packed bed reactor treating distillery waste with a COD of 30 g/l (95 % in soluble form) are presented. The digester contains 4300 m3 of packing, and is operational six months a year. It is one of Europe's largest units using this technique. After a few problems with fixing the biomass on start-up, organic loading has been regularly increased, reaching an average of 6 kg COD/m3.d during the 2nd year and 10 to 12 kg COD/m3.d during the 4th year, with soluble COD reductions of 90 to 95 %. The biomass released into the treated effluent was in the region of 0.15 kg SS/kg COD eliminated in the latter campaign. Overall performance in the 2nd, 3rd and 4th seasons are presented and discussed. The stability of digestion was studied over the whole of the 2nd and 4th seasons using measures of VFA at various levels within the reactor. Tracer study was conducted at the end of 2nd year to characterize the hydraulic behavior of the reactor. Results indicated a flow pattern close to a complete mixing and dead space was in the region of 20 % of liquid volume.

Effect of C/N/P Ratio on the Performance of a Downflow Stationary Fixed Film Reactor (DSFFR) Working at Low Organic Loading Rates

Effect of C/N/P Ratio on the Performance of a Downflow Stationary Fixed Film Reactor (DSFFR) Working at Low Organic Loading Rates

Anaerobic-aerobic treatment of distillery wastes

In this study an attempt has been made to find a solution to the problem of disposal of distillery effluents through anaerobic followed by aerobic treatment. Accordingly, experimental studies were planned and carried out in two phases. The first phase experimentation was conducted to study the performance of Semicontinuous Fixed Film Anaerobic Reactors (SCFFAR) which simulate Downflow Stationary Fixed Film anaerobic reactors (DSFF) for partial treatment of distillery waste. Second phase experimentation included studies on degradation of anaerobically treated effluent employing semicontinuous aerobic reactors with sludge recycle. The results indicated that the distillery waste should be diluted to bring down the COD to about 50 000 mg L−1 before the same is treated by stationery fixed film anaerobic reactors and this dilution can be achieved by circulating the treated effluent. Further the reduction of COD beyond 9000 to 10 000 mg L−1 by anaerobic treatment appears to be uneconomical. Results of second phase of the study show that the aerobic degradation of anaerobically treated effluent can achieve significant COD reduction (approx. 67%). However, reduction of COD of final effluent below 500 mg L−1 appears to be very difficult. The settling characteristics of the sludge produced in aerobic study depended on the BSRT value and improved with increase in BSRT.

Startup of anaerobic downflow stationary fixed film (DSFF) reactors

One of the serious problems limiting the application of full-scale anaerobic fixed film processes is reactor startup. To better understand startup, studies with downflow stationary fixed film (DSFF) reactors were conducted to characterize the effects of influent concentration, support material, and surface-to-volume ratio on biofilm development and overall reactor performance. Materials with roughened surfaces gave the best startup performance and as expected increased surface area in the reactors led to more rapid increases in loading rates and higher ultimate loadings. Soluble influent COD concentrations between 5 x 10(3) and 2 x 10(4) mg/L influenced the rate of biofilm development. Lower COD concentrations resulted in faster development of the biofilm, even though ultimate loadings were not necessarily achieved as rapidly as in reactors fed higher strength wastes. No decrease in specific activity of the biofilms in each reactor was observed as the thickness of the biofilms increased to their maximum value at the ultimate loadings. The operation of reactors fed lower strength wastes was more stable than reactors receiving higher strength feeds at comparable loadings. Biofilm yield and activity, COD removals, suspended growth and activity, and other system parameters are discussed.

Effect of reactor height on mixing characteristics and performance of the anaerobic downflow stationary fixed-film (DSFF) reactor

Three anaerobic downflow stationary fixed-film (DSFF) reactors using multiple vertical clay channels of different heights (31, 92 and 183 cm) and treating bean blanching waste showed improved performance and mixing characteristics with increased reactor height. A start-up period of 100 days was necessary to achieve the best performance in terms of loading rate (up to 9.5 kg Chemical Oxygen Demand (COD) m −3 d −1) and methane production rate (up to 2.7 m 3 m −3 d −1). During this period, differences in performance could only be related to the surface-to-volume ratio. At steady-state, mixing analysis indicated that the reactors deviated from the perfect-mixed pattern. Some dead space and shortcircuiting occurred. The amount of dead space due to biomass accumulation decreased as the reactor height increased (up to 44% for the shortest reactor). The COD removal efficiency was dependent on loading rate, decreasing from 90% at a loading rate of 1.0 kg COD m −3 d −1 to 75% at 7.0 kg COD m −3 d −1. However, the effect was more pronounced in the shortest reactor than in the tallest one. The improvement in mixing characteristics in the tallest reactor could be related to the higher liquid velocity inside channels which in turn permitted better support utilization and concomitant better COD removal. Data also suggest that it may be preferable to scale-up vertically rather than horizontally in order to maximize the liquid velocity in the channels.

Mixing characteristics and startup of anaerobic downflow stationary fixed film (DSFF) reactors

Tests to determine the mixing characteristics of the anaerobic downflow stationary fixed film (DSFF) reactor during startup showed that mixing characteristics affected performance. Different mixing profiles were obtained by keeping the same flow distribution system and by varying the number of clay channels (1, 4, and 25) in the DSFF reactors (2-32 L). Results with a clean bed reactor indicated a plug flow pattern with a relatively large extent of dispersion. Recirculation dramatically improved the mixing and the residence time distribution (RTD) changed to that of the completely mixed type. Multiple-channel reactors exhibited a dead space of ca. 12% of the total volume, likely a result of a less than optimally designed flow distributor. A startup period of 90 days was necessary to achieve a maximum loading rate of between 10 and 15 kg COD/m(3) day, a volumetric methane production rate of up to 3 m(3) (STP)/m(3) day and a COD reduction efficiency of up to 90%. For the first 50 days of operation, the difference in achievable volumetric loading rate and volumetric methane production rate was only related to the surface-to-volume ratio of the reactors and was not affected by the number of channels present. After 90 days, the bacterial growth on the support material was sufficient to dramatically increase the amount of dead space in the reactors, especially in multiple-channel reactors (up to 55% of their volume). As a result, the performance of these reactors deteriorated and overloading characteristics were observed. Other results showed that biogas production alone was not sufficient to improve reactor mixing and that little or no shortcircuiting or channelling occurred. Furthermore, the nonmethanogenic bacterial activity in the liquid phase was not affected by the degree of mixing but acetoclastic methanogenic and hydrogenophilic methanogenic activity in the liquid phase were reduced as the fluid flow pattern in the reactor improved.

Stability and performance of mesophilic anaerobic fixed‐film reactors during organic overloading

The stability of downflow stationary fixed-film (DSFF) reactors was evaluated under extreme organic shock loads. Reactors could handle five- to sevenfold increases in organic loading and recover to normal performance in a relatively short period of time (usually 24-72 h) during treatment of well-buffered sucrose and acetic acid wastewater at 27 and 35 degrees C. Overloading was characterized by elevated volatile-acid concentrations, decreased reactor pH, and excess biofilm sloughing. Reactors could not cope with extreme organic shocks during treatment of poorly buffered sucrose wastewater. The pH of the mixed liquor was observed to be a more important factor than the volatile-acid concentration in determining whether DSFF reactors would recover in a reasonable period of time.

Effect of effluent recirculation on start-up and steady state operation of the downflow stationary fixed film (DSFF) reactor

In this study, the effect of effluent recirculation on the start-up and steady state operation of the DSFF is reported. Recirculation had little effect on start-up; however, the maximum loading rate which could be applied to the reactor was higher at higher rates of effluent recirculation.

Treatment of fish processing waste using the downflow stationary fixed film (DSFF) reactor

The DSFF reactor has been shown to be capable of treating a wide variety of wastes. In this study, a high protein fish processing waste was treated at several influent concentrations. Chemical oxygen demand (COD) removal efficiencies of up to 90% were achieved at loading rates in excess of 10 kg COD/m3/day.

Effect of hydraulic and organic overloading on thermophilic downflow stationary fixed film (DSFF) reactor

Tests to determine the stability of thermophilic DSFF reactors using bean blanching waste as substrate, showed them to become unstable at 30 to 40 kg/m3/day whether hydraulically or organically overloaded. This level is significantly less than mesophilic reactors could handle (90 kg/m3/day).