The anaerobic treatment of soft drink wastewater in UASB and hybrid reactors

The anaerobic treatment of soft drink wastewater (SDW) was studied in two laboratory reactors—a 1.8-L UASB reactor and a 3-L hybrid reactor-sludge bed containing a layer of polyurethane in the upper part, at 35°C. The highest organic loading rates (OLR) achieved were 13 and 16.5 g COD/L · D for hybrid and UASB reactors, respectively, with the treatment efficiency of about 80% for both reactors. Despite the higher treatment productivity achieved for the UASB reactor, its lower ability to generate a sufficient level of alkalinity led to difficulties in maintaining a stable operation performance. Therefore, the hybrid reactor seems to be indicated for OLR higher than 10 g COD/L · d and HRT lower than 1 D, from the point of view of reliability of these two systems. Both reactors can treat the SDW with pH influent up to 11.0. The feeding of reactors with higher pH influent values led to their quick failure because of alkali shock. The duration of the recovery period after alkali shock was about 1.5-2 mo.     

Two-step upflow anaerobic sludge bed system for sewage treatment under subtropical conditions with posttreatment in waste stabilization ponds

A pilot-scale sewage treatment system consisting of two upflow anaerobic sludge bed (UASB) reactors followed by five waste stabilization ponds (WSPs) in series was studied under subtropical conditions. The first UASB reactor started up in only 1 mo (stable operation, high chemical oxygen demand [COD] removal efficiency, low volatile fatty acids concentration in the effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm3/kg of CODremoved). Removal efficiencies up to 90% were obtained in the anaerobic steps at a hydraulic retention time of 6 + 4 h (80% removal in the first step). Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobic steps and 99.98% in WSPs). COD balances over UASB reactors are provided. A minimum set of data necessary to build COD balances is proposed. Intermittent sludge washout was detected in the reactors with the COD balances. Sludge washout from single-step UASB reactors should be monitored and minimized in order to ensure constant compliance with discharge standards, especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions.     

Feasibility of treating swine manure in an anaerobic sequencing batch biofilm reactor with mechanical stirring

Anaerobic sequencing batch reactors containing granular or flocculent biomass have been employed successfully in the treatment of piggery wastewater. However, the studies in which these reactors were employed did not focus specifically on accelerating the hydrolysis step, even though the degradation of this chemical oxygen demand (COD) fraction is likely to be the limiting step in many investigations of this type of wastewater. The mechanically stirred anaerobic sequencing batch biofilm reactor offers an alternative for hastening the hydrolysis step, because mechanical agitation can help to speed up the reduction of particle sizes in the fraction of particulate organic matter. In the present study, a 4.5-L reactor was operated at 30°C, with biomass immobilized on cubic polyurethane foam matrices (1 cm of side) and mechanical stirring provided by three flat-blade turbines (6 cm) at agitation rates varying from 0 to 500 rpm. The reactor was operated to treat diluted swine waste, and mechanical stirring efficiently improved degradation of the suspended COD. The operational data indicate that the reactor remained stable during the testing period. After 2 h of operation at 500 rpm, the suspended COD decreased by about 65% (from 1500 to 380 mg/L). Apparent kinetic constants were also calculated by modified first-order expressions.     

One- and two-stage upflow anaerobic sludge-bed reactor pretreatment of winery wastewater at 4–10°C

The operating performance of a single and two (in series) laboratory upflow anaerobic sludge-bed (UASB) reactors (2.7-L working volume, recycle ratio varied from 1:1 to 1:18) treating diluted wine vinasse was investigated under psychrophilic conditions (4-10 degreesC). For a single UASB reactor seeded with granular sludge, the average organic loading rates (OLRs) applied were 4.7, 3.7, and 1.7 g of chemical oxygen demand (COD)/(L.d) (hydraulic retention times [HRTs] were about 1 d) at 9-11, 6 to 7, and 4 to 5 degreesC, respectively. The average total COD removal for preacidified vinasse wastewater was about 60% for all the temperature regimes tested. For two UASB reactors in series, the average total COD removal for treatment of non-preacidified wastewater exceeded 70% (the average OLRs for a whole system were 2.2, 1.8, and 1.3 g of COD/[L.d] under HRTs of 2 d at 10, 7, and 4 degreesC, respectively). In situ determinations of kinetic sludge characteristics (apparent Vm and Km) revealed the existence of substantial mass transfer limitations for the soluble substrates inside the reactor sludge bed. Therefore, application of higher recycle ratios is essential for enhancement of UASB pretreatment under psychrophilic conditions. The produced anaerobic effluents were shown to be efficiently posttreated aerobically: final effluent COD concentrations were about 0.1 g/L. Successful operation of the UASB reactors at quite low temperatures (4-10 degreesC) opens some perspectives for application of high-rate anaerobic pretreatment at ambient temperatures.     

Evaluation of bacterial detachment rates in porous media

The ability of published biomass detachment rate expressions to describe experimental data obtained from porous media reactors usingPseudomonas aeruginosa grown aerobically on glucose was evaluated. A first-order rate expression on attached biomass concentration best reflected effluent substrate concentration for combined data sets. Detachment rate coefficientk _d1 was dependent on initial substrate concentration. Simulation of porous media reactor experiments indicated that responses using higher influent substrate concentrations possessed greater sensitivity to variations ink _d1. Simulations of field bioremediation systems suggest the use of accurate biofilm development kinetics is important in the prediction of well bore biofouling.     

AnSBBR Applied to a Personal Care Industry Wastewater Treatment: Effects of Fill Time,Volume Treated Per Cycle,and Organic Load

A study was performed regarding the effect of the relation between fill time, volume treated per cycle, and influent concentration at different applied organic loadings on the stability and efficiency of an anaerobic sequencing batch reactor containing immobilized biomass on polyurethane foam with recirculation of the liquid phase (AnSBBR) applied to the treatment of wastewater from a personal care industry. Total cycle length of the reactor was 8 h (480 min). Fill times were 10 min in the batch operation, 4 h in the fed-batch operation, and a 10-min batch followed by a 4-h fed batch in the mixed operation. Settling time was not necessary since the biomass was immobilized and decant time was 10 min. Volume of liquid medium in the reactor was 2.5 L, whereas volume treated per cycle ranged from 0.88 to 2.5 L in accordance with fill time. Influent concentration varied from 300 to 1,425 mg COD/L, resulting in an applied volumetric organic load of 0.9 and 1.5 g COD/L.d. Recirculation flow rate was 20 L/h, and the reactor was maintained at 30 °C. Values of organic matter removal efficiency of filtered effluent samples were below 71% in the batch operations and above 74% in the operations of fed batch followed by batch. Feeding wastewater during part of the operational cycle was beneficial to the system, as it resulted in indirect control over the conversion of substrate into intermediates that would negatively interfere with the biochemical reactions regarding the degradation of organic matter. As a result, the average substrate consumption increased, leading to higher organic removal efficiencies in the fed-batch operations.     

Strategies in lipase production by immobilizedCandida rugosa cells

Growing cells ofCandida rugosa immobilized in polymethacrylamide-hydrazide and polyurethane foam were employed in fluidized and packed bed reactors, for discontinuous and continuous fermentations to obtain extracellular lipase. In spite of hydrodynamic problems, fermentation cultures using polyurethane foam showed higher lipolytic activity than cultures employing polymethacrylamide-hydrazide beads, which was probably owing to the high immobilized biomass concentration in polyurethane observed by direct microscopy enumeration. Different oleic acid concentrations were assayed. The maximum level of lipase was achieved at 4 g/L of oleic acid. These results reaffirm that lipase production is a direct function of cell-substrate contact and that the organic substrate dispersion is important in this system.     

The Use of Seaweed and Sugarcane Bagasse for the Biological Treatment of Metal-contaminated Waters Under Sulfate-reducing Conditions

When wetlands reach maximum treatment capacity to remove heavy metals, removal can still take place through precipitation as sulfide because of the biological reduction of sulfate. To achieve this goal, anaerobic conditions must be attained, a sulfate source must exist, and an adequate substrate for sulfate-reducing bacteria (SRB) is also required. In the present work, two ligneous-cellulosic materials, a brown seaweed and sugarcane bagasse, have been selected as substrates for SRB growth. Experiments were simultaneously conducted in continuous operation in two columns (0.57 L each), one containing the ligneous-cellulosic material plus inoculum and another containing only the ligneous-cellulosic material. In this work, the removal of cadmium and zinc was studied because of their presence in effluents from mining/metallurgy operations. Results obtained indicated that the inoculated reactor was able to treat the effluent more efficiently than the noninoculated reactor considering the time course of the tests.     

AnSBBR Applied to the Treatment of Metalworking Fluid Wastewater: Effect of Organic and Shock Load

An investigation was performed regarding the application of a mechanically stirred anaerobic sequencing batch biofilm reactor containing immobilized biomass on inert polyurethane foam (AnSBBR) to the treatment of soluble metalworking fluids to remove organic matter and produce methane. The effect of increasing organic matter and reactor fill time, as well as shock load, on reactor stability and efficiency have been analyzed. The 5-L AnSBBR was operated at 30?°C in 8-h cycles, agitation of 400 rpm, and treated 2.0 L effluent per cycle. Organic matter was increased by increasing the influent concentration (500, 1,000, 2,000, and 3,000 mg chemical oxygen demand (COD)/L). Fill times investigated were in the batch mode (fill time 10 min) and fed-batch followed by batch (fill time 4 h). In the batch mode, organic matter removal efficiencies were 87%, 86%, and 80% for influent concentrations of 500, 1,000, and 2,000 mgCOD/L (1.50, 3.12, and 6.08 gCOD/L.d), respectively. At 3,000 mgCOD/L (9.38 gCOD/L.d), operational stability could not be achieved. The reactor managed to maintain stability when a shock load twice as high the feed concentration was applied, evidencing the robustness of the reactor to potential concentration variations in the wastewater being treated. Increasing the fill time to 4 h did not improve removal efficiency, which was 72% for 2,000 mgCOD/L. Thus, gradual feeding did not improve organic matter removal. The concentration of methane formed at 6.08 gCOD/L was 5.20 mmolCH₄, which corresponded to 78% of the biogas composition. The behavior of the reactor during batch and fed-batch feeding could be explained by a kinetic model that considers organic matter consumption, production, and consumption of total volatile acids and methane production.     

Radon as a tracer to determine the mean residence times of groundwater in decontamination reactors

The groundwater at a former gasoline production site in Germany is heavily contaminated with aromatic hydrocarbons (mostly benzene) and is currently being treated in bioreactors under anaerobic conditions. To determine the reaction kinetics it is essential to know the mean residence time of the groundwater in these reactors. Most of the commonly used tracers (dyes and salts) did not give reliable results because of their interaction with the mineral matrix in the reactors. In this study radon (²²²Rn) dissolved in the groundwater is used as the tracer. The flow rate of groundwater through the reactors is 1 l/h. Over a period of 8 hours the radon-spiked groundwater was injected into the natural groundwater which has a very low radon concentration. The radon concentration of the discharged water is measured online at the reactor outlet. An increasing radon concentration at the reactor exit indicates the shortest residence time of the water. The time-dependent progress of the radon concentration provides detailed information about the flow behavior and residence times of water in the reactor.     

Effect of Fill Time on the Performance of Pilot-scale ASBR and AnSBBR Applied to Sanitary Wastewater Treatment

Many lab-scale studies have been carried out regarding the effect of feed strategy on the performance of anaerobic sequencing batch reactors (ASBR); however, more detailed pilot-scale studies should be performed to assess the real applicability of this type of operation. Therefore, the objective of this work was to assess the effect of feed strategy or fill time in a 1-m³ mechanically stirred pilot-scale sequencing batch reactor, treating 0.65 m³ sanitary wastewater in 8-h cycles at ambient temperature. Two reactor configurations were used: one containing granular biomass (denominated ASBR) and the other immobilized biomass on polyurethane foam as inert support (denominated anaerobic sequencing batch biofilm reactor (AnSBBR)). The reactors were operated under five distinct feed strategies, namely: typical batch and fed-batch for 25%, 50%, 75%, and 100% of the cycle length. Stirring frequency in the ASBR was 40 rpm with two flat-blade turbine impellers and 80 rpm in the AnSBBR with two helix impellers. The results showed that both the ASBR and AnSBBR when operated under typical batch, fed-batch for 50% and 75% of the cycle length, presented improved organic matter removal efficiencies, without significant differences in performance, thus showing important operational flexibility. In addition, the reactors presented operation stability under all conditions.     

Energy generation by methanation of persistent wastes

A 15-L anaerobic fixed-film reactor (AFFR) was evaluated for treating a trade effluent containing inhibitory concentrations of persistent branched-chain fatty acids, namely 2-ethylhexanoic acid (2-EHA) and neopentanoic acid (NPA), at a total of 17,000 mg COD/L. The AFFR was packed with fire-expanded clay spheres, and start-up was accomplished in 60 d. The organic load was increased in steps from 1.1 to 8.5 g COD/L/d. Total COD, 2-EHA, and NPA removal efficiencies were maintained above 70, 98, and 75%, respectively. The reactor could recover from a shock load of 150% increase in organic load. Combined mechanisms of organic adsorption and biodegradation rendered the AFFR more stable with shock loads. Mathane gas produced from the process could be used for preheating the effluent.     

Effect of Substrate Concentration on Dark Fermentation Hydrogen Production Using an Anaerobic Fluidized Bed Reactor

The effect of substrate (glucose) concentration on the stability and yield of a continuous fermentative process that produces hydrogen was studied. Four anaerobic fluidized bed reactors (AFBRs) were operated with a hydraulic retention time (HRT) from 1 to 8 h and an influent glucose concentration from 2 to 25 g L⁻¹. The reactors were inoculated with thermally pre-treated anaerobic sludge and operated at a temperature of 30 °C with an influent pH around 5.5 and an effluent pH of about 3.5. The AFBRs with a HRT of 2 h and a feed strength of 2, 4, and 10 g L⁻¹ showed satisfactory H₂ production performance, but the reactor fed with 25 g L⁻¹ of glucose did not. The highest hydrogen yield value was obtained in the reactor with a glucose concentration of 2 g L⁻¹ when it was operated at a HRT of 2 h. The maximum hydrogen production rate value was achieved in the reactor with a HRT of 1 h and a feed strength of 10 g L⁻¹. The AFBRs operated with glucose concentrations of 2 and 4 g L⁻¹ produced greater amounts of acetic and butyric acids, while AFBRs with higher glucose concentrations produced a greater amount of solvents.     

High-performance bioreactors: a new generation

Compact loop bioreactors with a total volume of 4 l were equipped with electrically controllable valves and pumps, most of the currently available on-line sensors, direct digital control systems and a process minicomputer; complete automatic operation was thus achieved. These reactors perform excellently: the mixing time is <1 s, oxygen transfer is not a limiting factor and the precision of control of more than 10 process variables is much better than so far reported on other systems. Such high-performance bioreactors were used in investigating the stable synchronous oscillations of Saccharomyces-type yeasts and the reduction of slightly soluble organic compounds with biocatalysts. The inherent advantages of on-line measurement (and control) are discussed.     

Removal of Nitrogen and Organic Matter in a Radial-Flow Aerobic-Anoxic Immobilized Biomass Reactor Used in the Posttreatment of Anaerobically Treated Effluent

This work reports on the removal of organic matter and nitrogen in a radial-flow aerobic-anoxic immobilized biomass (RAIB) reactor fed with domestic sewage pretreated in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor. Polyurethane foam was used as support material for biomass attachment in both reactors. In batch experiments, a first-order kinetic model with residual concentration represented the organic matter removal rate, whereas nitrogen conversion followed a pseudo-first-order reaction in series model, with kinetic constants k ₁ (ammonium to nitrite) and k ₂ (nitrite to nitrate) of 0.25 and 6.62 h⁻¹, respectively. The RAIB reactor was operated in continuous-flow mode and changes in the airflow rate and hydraulic retention time were found to interfere in the apparent kinetic constants to the nitritation (k ₁) and nitratation (k ₂). Nitrification and denitrification were achieved in the partially aerated RAIB reactor operating with hydraulic retention times of 3.3 h and 2.7 h in the aerobic and anoxic zones, respectively. Ethanol was added in the anoxic zone of the reactor to promote denitrification. The effluent flow of the RAIB reactor presented a COD of 52 mg l⁻¹, and concentrations of 2 mg , 1.24 mg and 3.46 mg .     

Granulation of activated sludge in a laboratory upflow sludge blanket reactor

The creation of anoxic granulated biomass has been monitored in a laboratory USB (Upflow Sludge Blanket) reactor with the volume of 3.6 L. The objective of this research was to verify the possibilities of post-denitrification of residual NO₃-N concentrations in treated wastewater (denitrification of 10-20 mg L⁻¹ NO₃-N) and to determine the maximum hydraulic and mass loading of the granulated biomass reactor. G-phase from biodiesel production and methanol were both tested as external organic denitrification substrates. The ratio of the organic substrate COD to NO₃-N was 6. Only methanol was proven as a suitable organic substrate for this kind of reactor. However, the biomass adaptation to the substrate took over a week. The cultivation of anoxic granulated biomass was reached at hydraulic loading of over 0.35 m h⁻¹. The size of granules was smaller when compared with results found and described in literary reports (granules up to 1 mm); however, settling properties were excellent and denitrification was deemed suitable for the USB reactor. Sludge volume indexes of granules ranged from 35-50 mL g⁻¹ and settling rates reached 11 m h⁻¹. Maximum hydraulic and mass loadings in the USB reactor were 0.95 m3 m⁻² h⁻¹ and 6.6 kg m⁻³ d⁻¹. At higher loading levels, a wash-out of the biomass occurred. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

Two-phase methanization of food wastes in pilot scale

A 5 ton/d pilot scale two-phase anaerobic digester was constructed and tested to treat Korean food wastes in Anyang city near Seoul. The easily degradable presorted food waste was efficiently treated in the two-phase anaerobic digestion process. The waste contained in plastic bags was shredded and then screened for the removal of inert materials such as fabrics and plastics, and subsequently put into the two-stage reactors. Heavy and light inerts such as bones, shells, spoons, and plastic pieces were again removed by gravity differences. The residual organic component was effectively hydrolyzed and acidified in the first reactor with 5 d space time at pH of about 6.5. The second, methanization reactor converted the acids into methane with pH between 7.4 and 7.8. The space time for the second reactor was 15 d. The effluent from the second reactor was recycled to the first reactor to provide alkalinities. The process showed stable steady-state operation with the maximum organic loading rate of 7.9 kg volatile solid (VS)/m³/d and the volatile solid reduction efficiency of about 70%. The total of 3.6 tons presorted MSW containing 2.9 tons of food organic was treated to produce about 230 m³ of biogas with 70% (v/v) of methane and 80 kg of humus. This process is extended to full-scale treating 15 tons of food waste a day in Euiwang city and the produced biogas is utilized for the heating/cooling of adjacent buildings. Author to whom all correspondence and reprint requests should be addressed.     

Continuous biotreatment of copper-concentrated solutions by biosorption with Sargassum sp.

Seaweed Sargassum sp. biomass proved to be useful for the recovery of ionic copper from highly concentrated solutions simulating effluents from semiconductor production. In the case of solutions containing copper in the form of chloride, sulfate, and nitrate salts, the best pH for the recovery of copper was 4.5. It was observed that copper biosorption from copper nitrate solutions was higher than the recovery of copper from copper chloride or copper sulfate solutions. The continuous system used was constituted of four column reactors filled with the biomass of Sargassum sp. and showed high operational stability. The biomass of Sargassum sp. in the reactors was gradually saturated from the bottom to the top of each column reactor. The biomass of Sargassum sp. in the first column saturated first, followed by a gradual saturation of the remaining columns owing to preconcentration performed by the biomass in the first column. The biomass of Sargassum in the bioreactors completely biosorbed the ionic copper contained in 63 L of copper sulfate solution, 72 L of copper chloride solution, and 72 L of copper nitrate solution, all the solutions containing copper at 500 mg/L. Effluents produced after biosorption presented copper concentrations < 0.5 mg/L.     

Inhibition effect of free ammonia and free nitrous acid on nitrite-oxidising bacteria during sludge liquor treatment: influence of feeding strategy

The importance of feeding strategy for the long-term selective inhibition of nitrite-oxidising bacteria (NOB) was demonstrated by comparison of laboratory-scale bioreactors: Completely Stirred Tank Reactor (CSTR) and Sequencing Batch Reactor (SBR). Moreover, the effect of the change of reactor operation regime from CSTR to SBR was demonstrated. Sludge liquor containing ammonia nitrogen in a range of 970–1500 mg L^?1 was the influent of the reactors. The experiments were performed at (23 ± 2)°C, with high concentration of dissolved oxygen (up to 8 mg L^?1) and with unlimited sludge retention time. In the SBR, permanent restriction of NOB activity was achieved for more than 700 days by the strong inhibition effect of fluctuating concentrations of free ammonia and free nitrous acid during the operational cycles of SBR. In contrast, nitrite-oxidising bacteria were able to gradually adapt to the conditions prevailing in CSTR and produce nitrate although the concentration of free ammonia and free nitrous acid significantly exceeded inhibition limits for NOB activity in this system. Transferring the reactor operation regime from CSTR to SBR resulted in immediate and permanent inhibition of NOB activity in the reactor.     

Sustainable treatment and reuse of diluted pig manure streams in Russia: from laboratory trials to full-scale implementation

This article summarizes the results obtained during the laboratory and pilot development of integrated biologic and physicochemical treatment and reuse of diluted pig manure streams. The application of a straw filter was an effective means to separate the solid and liquid fractions of raw wastewater and resulted in the removal of a significant part of the dry matter, total nitrogen, and phosphorus (65, 27, and 32%, respectively). From the filtrate generated, 60–80% of the total chemical oxygen demand (COD) was removed in an upflow anaerobic sludge bed reactor operating at 15–30°C. Ammonia was efficiently eliminated (>99%) from the anaerobic effluents using Ural laumantite as an ion exchanger. However, the nitrogen-content of the zeolite was too low to consider this method of ammonia removal economically feasible. The phosphate precipitation block, consisting of stripper of CO₂ and fluidized-bed crystallizator, was able to decrease the concentration of soluble phosphate in the anaerobic effluents up to 7–15 mg of phosphate/L. The application of aerobic/anoxic biofilter as a sole polishing step was acceptable from an aesthetic point of view (the effluents were transparent and almost colorless and odorless) and elimination of biochemical oxygen demand (the resting COD was hardly biodegradable). However, the effluent nutrient concentrations (especially nitrogen) were far from the current standards for direct discharge of treated wastewater. We discuss the approaches for further improvement of effluent quality. Finally, we provide an outline of a full-scale system that partially implements the laboratory- and pilot-scale results obtained.