Pilot-scale Biofilm Reactor Research Articles

Simultaneous Removal of Soluble Metal Species and Nitrate from Acidic and Saline Industrial Wastewater in a Pilot-Scale Biofilm Reactor

The hydrometallurgical treatment of waste printed circuit boards for the recovery of precious metals generates acidic wastewater containing nitrate, chloride and residual base metals. The scope of this work is the study of a biological treatment process for the concurrent metal sequestering, nitrate reduction and wastewater neutralization. A pilot-scale packed-bed biofilm reactor was set up, inoculated with the strain H. denitrificans and experimentally monitored. The range of operating parameters examined included: (a) nitrate concentration 750–5750 mg/L NO3−; (b) pH 3–8; (c) Cu, Ni, Zn and Fe at 50 mg/L and 100 mg/L; and (d) chloride concentration 5%–10% as NaCl. The presence of metals did not affect denitrification at the concentrations examined. H. denitrificans completely reduced nitrate and the intermediately produced nitrite at elevated chloride levels. Denitrification shifted pH towards circumneutral to alkaline values, where iron, zinc, copper and nickel were sequestered quantitatively from solution via bioprecipitation. The proposed simple, robust and low-cost biological treatment unit is advantageous compared to the conventional wastewater treatment, where metal precipitation is based on chemical neutralization and the problem of nitrate removal remains unresolved.

Response of performance and bacterial community to oligotrophic stress in biofilm systems for raw water pretreatment.

Understanding the dynamics of performance and bacterial community of biofilm under oligotrophic stress is necessary for the process optimization and risk management in biofilm systems for raw water pretreatment. In this study, biofilm obtained from a pilot-scale biofilm reactor was inoculated into a pilot-scale experimental tank for the treatment of oligotrophic raw water. Results showed that the removal of NH4+-N was impaired in biofilm systems when influent NH4+-N was less than 0.35mg L-1 or NH4+-N loading rate of less than 7.51mg L-1 day-1. The dominant bacteria detected in biofilm of different carrier were obvious distinct from phylum to genus level under oligotrophic stress. The dominant bacteria in elastic stereo media carrier changed from Proteobacteria (51.1%) to Firmicutes (32.7%), while Proteobacteria was always dominant in suspended ball carrier after long-term operation under oligotrophic conditions. Oligotrophic stress largely decreased the functional bacteria for the removal of nitrogen and organics including many genera in Proteobacteria and Nitrospirae, but increased several genera with spore forming organisms or potential bacterial pathogens in ESM carrier mainly including Bacillus, Mycobacterium, Pseudomonas, etc.

Startup pattern and performance enhancement of pilot-scale biofilm process for raw water pretreatment

The quality of raw water is getting worse in developing countries because of the inadequate treatment of municipal sewage, industrial wastewater and agricultural runoff. Aiming at the biofilm enrichment and pollutant removal, two pilot-scale biofilm reactors were built with different biological carriers. Results showed that compared with the blank carrier, the biofilm was easily enriched on the biofilm precoated carrier and less nitrite accumulation occurred. The removal efficiencies of NH4+-N, DOC and UV254 increased under the aeration condition, and a optimum DO level for the adequate nitrification was 1.0–2.6mgL−1 with the suitable temperature range of 21–22°C. Study on the trihalomethane prediction model indicated that the presentence of algae increased the risk of disinfection by-products production, which could be effectively controlled via manual algae removing and light shading. In this study, the performance of biofilm pretreatment process could be enhanced under the optimized condition of DO level and biofilm carrier.

Fouling and structural changes of Shirasu porous glass (SPG) membrane used in aerobic wastewater treatment process for microbubble aeration

In the present study a hydrophilic SPG membrane was used for microbubble generation to aerate a pilot-scale biofilm reactor treating synthetic municipal wastewater. The external fouling of SPG membrane was observed and identified during continuous operation of the bioreactor. Then the SPG membrane was cleaned offline by ultrasonic, thermal and acid treatment to remove fouling layer, organic and inorganic foulants on the membrane surface. The structural changes of SPG membrane were investigated after fouling and offline cleaning, using scanning electron microscopy (SEM), mercury and gas adsorption porosimetry, X-ray Diffraction (XRD), and Infrared (IR) absorption. SEM tests clearly demonstrated that these offline cleaning methods were effective to clear membrane external fouling. There was no obvious change in membrane pore size distribution after SPG membrane fouling and offline cleaning, but the membrane porosity and pore surface area increased slightly. XRD and IR analysis also showed that rare inorganic or organic foulants deposited on the pore surface inside the membrane. Therefore, the external fouling was identified as the main mechanism of SPG membrane fouling used in aerobic wastewater treatment process. The microbubble generation and oxygen mass transfer deteriorated due to external fouling of SPG membrane, which recovered after membrane offline cleaning.

The Role of Bioflocculation on Suspended Solids and Particulate COD Removal in the Trickling Filter Process

Understanding that there is a significant presence of extracellular polymeric substances at the biofilm/wastewater interface and that the primary constituent of chemical oxygen demand (COD) in domestic wastewaters is organic particulates, this research describes the kinetics of particulate removal in a pilot-scale trickling filter (TF) and the role of bioflocculation in the removal process. Recent research has described the role of bioflocculation on particulate COD (PCOD) removal in suspended growth biological wastewater treatment systems. However, no research pertaining to PCOD removal by bioflocculation in attached growth systems was identified prior to this study. For this study, experiments were conducted using both bench- and pilot-scale biofilm reactors and provided evidence that the removal of organic and inorganic particulate matter in a TF bioreactor follows a first-order bioflocculation rate equation. The statistical analysis of data obtained from the pilot TF fits the dispersion model to suspended solids and PCOD remaining in the pilot TF.

Hydrolysis of organic wastewater particles in laboratory scale and pilot scale biofilm reactors under anoxic and aerobic conditions

Hydrolysis and degradation of particulate organic matter has been isolated and investigated in laboratory scale and pilot scale biofilters. Wastewater was supplied to biofilm reactors in order to accumulate particulates from wastewater in the filter. When synthetic wastewater with no organic matter was supplied to the reactors, hydrolysis of the particulates was the only process occurring. Results from the laboratory scale experiments under aerobic conditions with pre-settled wastewater show that the initial removal rate is high: rV, O2 = 2.1 kg O2/(m3 d) though fast declining towards a much slower rate. A mass balance of carbon (TOC/TIC) shows that only 10% of the accumulated TOC was transformed to TIC during the 12 hour long experiment. The pilot scale hydrolysis experiment was performed in a new type of biofilm reactor - the B2A® biofilter that is characterised by a series of decreasing sized granular media (80-2.5 mm). When hydrolysis experiments were performed on the anoxic pilot biofilter with pre-screened wastewater particulates as carbon source, a rapid (rV, NO3=0.7 kg NO3-N/(m3 d)) and a slowler (rV, NO3 = 0.3 kg NO3-N/(m3 d)) removal rate were observed at an oxygen concentration of 3.5 mg O2/l. It was found that the pilot biofilter could retain significant amounts of particulate organic matter, reducing the porosity of the filter media of an average from 0.35 to 0.11. A mass balance of carbon shows that up to 40% of the total incoming TOC accumulates in the filter at high flow rates. Only up to 15% of the accumulated TOC was transformed to TIC during the 24 hour long experiment.

Hydrolysis of organic wastewater particles in laboratory scale and pilot scale biofilm reactors under anoxic and aerobic conditions

Hydrolysis and degradation of particulate organic matter has been isolated and investigated in laboratory scale and pilot scale biofilters. Wastewater was supplied to biofilm reactors in order to accumulate particulates from wastewater in the filter. When synthetic wastewater with no organic matter was supplied to the reactors, hydrolysis of the particulates was the only process occurring. Results from the laboratory scale experiments under aerobic conditions with pre-settled wastewater show that the initial removal rate is high: rv, 02 = 2.1 kg 02/(m3 d) though fast declining towards a much slower rate. A mass balance of carbon (TOC/TIC) shows that only 10% of the accumulated TOC was transformed to TIC during the 12 hour long experiment. The pilot scale hydrolysis experiment was performed in a new type of biofilm reactor - the B2A® biofilter that is characterised by a series of decreasing sized granular media (80-2.5 mm). When hydrolysis experiments were performed on the anoxic pilot biofilter with pre-screened wastewater particulates as carbon source, a rapid (rv, NO3=0.7 kg NO3-N/(m3 d)) and a slower (rv, NO3 = 0.3 kg NO3-N/(m3 d)) removal rate were observed at an oxygen concentration of 3.5 mg O2/l. It was found that the pilot biofilter could retain significant amounts of particulate organic matter, reducing the porosity of the filter media of an average from 0.35 to 0.11. A mass balance of carbon shows that up to 40% of the total incoming TOC accumulates in the filter at high flow rates. Only up to 15% of the accumulated TOC was transformed to TIC during the 24 hour long experiment.

Operating characteristics of aerated submerged biofilm reactors for drinking water treatment

As the quality of raw water deteriorates, a number of additional treatment techniques have been developed and adapted to water treatment for producing a safe and aesthetically satisfactory drinking water. One of the various alternatives is to use a biological process, such as a submerged bed filter, as the first process in the treatment train followed by conventional treatment processes. Biofilm process for the pretreatment of water is suitable for advanced treatment as the biofilm can keep microorganism, at low organic concentrations. This article examines the application of biological treatment strategies to tackle the current problems of the water industry. Pilot-scale biofilm reactors were evaluated with various contaminants frequently encountered in water supplies. The studies focused on the production of biologically stable water, increased disinfectant stability, and reduced formation of disinfection by-products. Results showed that the finished water became more biologically stable even though the reduction of organics was relatively low. Biofilm grown on natural water supplies was effective in removing THMP (trihalomethane precursor) as well as taste and odour compounds, such as geosmin.

Operating characteristics of aerated submerged biofilm reactors for drinking water treatment

As the quality of raw water deteriorates, a number of additional treatment techniques have been developed and adapted to water treatment for producing a safe and aesthetically satisfactory drinking water. One of the various alternatives is to use a biological process, such as a submerged bed filter, as the first process in the treatment train followed by conventional treatment processes. Biofilm process for the pretreatment of water is suitable for advanced treatment as the biofilm can keep microorganism, at low organic concentrations. This article examines the application of biological treatment strategies to tackle the current problems of the water industry. Pilot-scale biofilm reactors were evaluated with various contaminants frequently encountered in water supplies. The studies focused on the production of biologically stable water, increased disinfectant stability, and reduced formation of disinfection by-products. Results showed that the finished water became more biologically stable even though the reduction of organics was relatively low. Biofilm grown on natural water supplies was effective in removing THMP (trihalomethane precursor) as well as taste and odour compounds, such as geosmin.