Downflow Stationary Fixed Film Reactors 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.

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 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 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 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

A kinetic study of the anaerobic digestion of piggery waste using down-flow stationary fixed film reactors

In this paper the behaviour of the down-flow stationary fixed film digesters is studied at laboratory and bench scale. Several organic loading rates are applied to the reactors in order to examine the support surface behaviour. Specific support surfaces of about 50 m2/m3 void volume seems to be optimal. A set of experiments carried out in a continuous stirred reactor is used to fit the kinetic constants of the Chen and Hashimoto's model. The model is then used to assess its applicability to the DSFF digesters. The results show that its application, is possible as a first approximation.

Diffusional limitations of anaerobic biofilms

Using an empirical determination of apparent kinetic parameters in the bulk mixed liquor, the intrinsic kinetic parameters of anaerobic biofilms developed at 35 °C during start-up and steady-state downflow stationary fixed film reactor operation were estimated. The apparent kinetic parameters of anaerobic biofilms are not significantly influenced by internal diffusion limitations. The apparent kinetic parameters of mature biofilms showed no significant trends with increased biofilm thickness up to 2.6 mm and increased apparent Thiele modulus up to 3.1. Key words: anaerobic, biofilm kinetics, Thiele modulus, wastewater, filter.

Steady State Kinetics of Anaerobic Downflow Stationary Fixed Film Reactors

Anaerobic downflow stationary fixed film reactors operated at 35°C successfully treated synthetic (sucrose based) wastewater of different concentrations at high organic loading rates and short hydraulic retention times. Based on observed relations between washout solids retention time, hydraulic retention time and loading rate, an empirical model of the process was formulated. Incorporation of the washout factor into accepted theory allowed good prediction of chemical oxygen demand removal efficiency and reactor biomass concentration.

Effects of terramycin and monensin on methanogenesis in DSFF reactors

The effects of terramycin (OTC) and monensin on methanogenesis were studied using batch activity tests and continuous-flow reactor experiments. Methanogenesis was not adversely affected by OTC but was inhibited by monesin in downflow stationary fixed film reactors at concentrations commonly found in manure. At relatively higher concentrations, monensin stopped methane production.

Integrated production of biogas and protein biomass from piggery manure

An integrated process involving the production of biogas and the recovery of proteins by anaerobic digestion of piggery manure has been studied. the digestion, effected in a 616 L downflow stationary fixed film reactor, resulted in a biogas production rate of approximately 0.86 m3 per m3 reactor per day (35°C, hydraulic retention time 7.2 days). Treatment of the digested effluent by flocculation, decantation and/or sieving yielded a solid biomass with reduced coliform counts and a protein content of about 14%.

Anaerobic treatment of beet waste in a stationary fixed-film reactor

Laboratory scale, downflow stationary fixed-film reactors with polyester cloth support and a surface-to-volume ratio of 86 m 2 m −3, operated continuously at 35°C, were capable of treating red beet wastewater with an organic strength between 5000 and 15 000 mg COD liter −1, at up to 87% COD removal efficiency. Organic loadings of up to 24 kg COD m −3 day −1 were achieved with COD removal rates of up to 16 kg COD m −3 day −1 and methane production rates exceeding 4 m 3 m −3 (reactor volume) day −1. Loadings of 30 kg COD m −3 day −1 and HRT of 5 h were achieved without process failure. The actual amount of waste organics converted and methane gas produced increased with increased loading, even though COD removal efficiencies decreased. A wide range of waste organic strengths could readily be treated but maximum methane production and COD conversion rates would be achieved with increased waste organic strength. Biomass yield increased with increased organic loading and was slightly influenced by waste organic strength.

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.

Anaerobic Downflow Stationary Fixed Film Reactors: Performance Under Steady-State and Non-Steady State Conditions

Performance of downflow stationary fixed film reactors depended on factors such as type of film support, film surface-to-volume ratio, height, temperature and fluid flow pattern. The downflow operation ensured the dilution of the waste as soon as it entered the reactor. Loading rates and organic removal efficiencies depended on the total amount of active biomass retained as well as on type of waste. For a wide variety of industrial wastes, including some of the forest industry, loading rates of 5 to 15 kg Chemical Oxygen Demand per m3 per day were readily obtained with removals of Chemical Oxygen Demand of 70-95%, depending on loading rate and type of waste. Severe hydraulic and organic overloadings were tolerated with operation back to normal, usually in 24 hours following cessation of adverse treatment. Reactors were operated with dilute and concentrated wastes (4000-130000 mg COD/1) and changed readily over from one waste to another. Intermittent loadings at high loading rates were also possible. Loading rates decreased linearly with temperatures between 35 and 10°C; at 10°C they were about 20% of those at 35°C. At thermophilic temperatures, loading rates and performance were similar to those at mesophilic temperatures. Results of a detailed study of mixing characteristics showed that mixing patterns, which depended on number of channels, their configuration and recirculation, affected performance noticeably.

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.

Development of a computer control system for anaerobic methane‐producing reactors

Anaerobic digestion processes with rapid production of methane are economical methods of waste stabilization. At the present time, these processes require highly trained technical staff and analytical equipment. The rudiments of a simple computer process control system are described to alleviate the need for analytical equipment and trained staff. Gas production was chosen as the controlled variable since it is a very sensitive indicator of digestor performance and can be measured rapidly. Feed rate was chosen as the manipulated variable. The aim was to develop a program which would maintain the performance of the process under normal operating conditions, and, in the event of a severe upset, would signal that a problem existed so remedial action could be taken. The digestor used was a down-flow stationary fixed film reactor. The waste used was a synthetic sugar waste containing 1% (w/v) sugar (10g chemical oxygen demand/L). The desired rate of biogas production was chosen as 250L/day at an approximate methane content of 50%.

Dairy Waste Treatment with Anaerobic Stationary Fixed Film Reactors

Cheese whey and a dilute waste from a cheese factory with a Chemical Oxygen Demand of 66,000 and 4,000 mg (COD)/L respectively, were treated at high loading rates in 0.7 to 1.2 L downflow anaerobic stationary fixed film reactors and an upflow sludge bed reactor. In downflow stationary fixed film reactors treating cheese whey, COD removal efficiencies of 97% were achieved at a loading rate of 5 kg COD/m3/day and 92% at a maximum loading rate of 22 kg COD/m3/day. With dairy plant waste, loading rates of up to 15 kg COD/m3/day were possible with COD removal efficiencies averaging 75%, decreasing slightly with increasing loading rates. In an upflow sludge bed reactor the COD removal efficiency of dairy plant waste, decreased from 87% at 5 kg COD/m3/day to 73% at 15 kg COD/m3/day. A stationary fixed film reactor treating a skim milk powder waste (4,000 ppm) could only be operated at up to 10 kg COD/m3/day with a treatment efficiency of 72%. Methane was produced from all wastes at rates corresponding to 0.32 m3 CH4 (0°C, 1 atm) per kg COD removed. Results show that stationary fixed film reactors are capable of treating dairy wastes at high loading rates and high COD removal efficiencies.

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).