Theoretical and experimental investigation of biodegradation of hydrocarbon polluted water in a three phase fluidized-bed bioreactor with PVC biofilm support

Treating organic cyanide-containing groundwater by immobilization of a nitrile-degrading bacterium with a biofilm-forming bacterium using fluidized bed reactors

Organic cyanide are widely used as an ingredient in the production of plastics, synthetic rubbers, polymers, pharmaceuticals and pesticides or used in laboratories and industries as solvents. Although nitrile-containing wastewater is subjected to primary and secondary treatments, residual nitriles may slowly seep and further migrate through groundwater, resulting in the micropollution of groundwater by organic pollutants. In this study, water samples were collected from different study areas in North China during a period of 3y (from 2013 to 2015) and analyzed to evaluate organic cyanide (CN^-) contamination in groundwater. Three parallel lab-scale fluidized bed reactors (FBRs) were tested for their ability to remove organic cyanide from groundwater. The organic cyanide concentration in groundwater increased significantly (P < 0.05) from 2013 to 2015. With an optimal hydraulic residence time (HRT) of 54 min, reactor R3 (inoculated with a nitrile-degrading bacterium, BX2, and a biofilm-forming bacterium, M1) effectively removed 99.8% of CN^- under steady operation, which was better than that of other reactors. Short-term shutdowns of FBRs had no serious effects on the efficiency of treating organic cyanide. This work demonstrated that the biofilm-forming bacterium could facilitate the fixation of nitrile-degrading bacterium and enhance the efficiency of removing organic cyanide from groundwater.

Synergistic effect of adsorption coupled with catalysis based on graphene-supported MOF hybrid aerogel for promoted removal of dyes

A three-dimensional MIL-100(Fe)/graphene hybrid aerogel (MG-HA) was fabricated via in situ decoration of graphene oxide with MIL-100(Fe) nanoparticles. The resulting MG-HA with interconnected pore structure was applied as both adsorbent and catalyst for the removal of methylene blue (MB) from aqueous solutions. The result shows that the saturation adsorption capacity of the MG-HA was as high as 333.33 mg g⁻¹, exceeding that of both the corresponding pristine graphene aerogel and MIL-100(Fe) nanoparticles. In the presence of hydrogen peroxide, MG-HA further exhibited catalytic degradation ability. The dual functions achieved a synergistic effect leading to the quick and complete removal of MB. The benefit was revealed in the treatment of high concentration of pollutants without leaving secondary pollution. The merit was intuitively demonstrated in the instant removal of MB through a model separation device in comparison with a series of common adsorbents. A feasible mathematic model was built based on the synergistic adsorption/catalysis process, which perfectly fitted the experimental data. A pseudo-second-order adsorption process and pseudo-first-order catalytic degradation kinetics were revealed. Additionally, the MG-HA was able to retain 93.4% of its initial removal efficiency after 5 cycles of application. The macro-material body can be easily separated and reused without a time-consuming and high-cost recycling process.

A three-dimensional MIL-100(Fe)/graphene hybrid aerogel was fabricated for highly efficient removal of dye pollutants via synergistic adsorption and degradation.

Laundry greywater treatment using a fluidized bed reactor: a proposed model based on greywater biodegradation and residence time distribution approach

The increasing demand for water and the decrease in global water resources require research into alternative solutions to preserve them. The present study deals with the optimization of a treatment process, i.e. an aerobic fluidized bed reactor and the modelling of the degradation that takes place within it. The methodology employed is based on the hydrodynamics of the treatment process linked to the biodegradation kinetics of greywater coming from a washing machine. The residence time distribution (RTD) approach is selected for the hydrodynamic study. Biodegradation kinetics are quantified by respirometry and dissolved organic carbon (DOC) analysis on several mass quantities of colonized particles. RTD determinations show that there are no dysfunctions in the fluidized bed. Its hydrodynamic behaviour is similar to the one of a continuous stirred-tank reactor. A first-order reaction is obtained from the DOC biodegradation study. A model describing the degradation that takes place into the reactor is proposed, and from a sensitive study, the influence of the operating conditions on DOC biodegradation is defined. The theoretical results calculated from the first-order equation C(t) = 0.593 x C(0) x e(-kt) are compared with the experimental results and validated by a Student test. The value of the kinetic constant k is 0.011 h(-1) in the presence of a biomass carrier. The results highlight that it is possible to design a reactor in order to obtain a carbon content lower than 15 mg C L(-1) when the characteristics of raw greywater are known.

Preparation of paper mill sludge-based granular activated carbon fillers for fluidized-bed bioreactor (FBBR)

Paper mill sludge (PMS) was utilized to prepare granular activated carbon (GAC) fillers for fluidized-bed bioreactor (FBBR) through stream activation. The properties of the PMS were tested and the optimum conditions for the production process were determined. Then, the GAC fillers were used in the FBBR to investigate the capacity for wastewater treatment. The results showed that the optimal conditions were: carbonization temperature of 450 degrees C, carbonization time of 50 min, activation temperature of 800 degrees C and activation time of 60 min. The specific surface area of the GAC fillers was 130 m2/g and the grain density was 1.34 x 10(3) kg/m3. The wastewater treatment results showed that after40 days ofrunning, under the conditions of influent COD of 800 mg/L and HRT of2 h, the COD removal efficiency was about 90%, which demonstrated that PMS-based GAC fillers were feasible for FBBR.

Optimization of an integrated sponge--granular activated carbon fluidized bed bioreactor as pretreatment to microfiltration in wastewater reuse

A specific integrated fluidized bed bioreactor (iFBBR) was optimized in terms of organic loading rate (OLR), hydraulic retention time (HRT) and frequency of new sustainable flocculant (NSBF) addition for primary treated sewage effluent (PTSE) treatment. It was observed that iFBBR achieved the best performance with the operating conditions of 4 times/day NSBF addition, HRT of 90 min and OLR of 8.64 kg COD/day m(3). The removal efficiencies were found to be more than 93% of dissolved organic carbon (DOC), 61% of total nitrogen (T-N) and 60% of total phosphorus (T-P). iFBBR as pretreatment of submerged microfiltration (SMF) is successful in increasing the critical flux and reducing the membrane fouling. NSBF-iFBBR-SMF hybrid system led to very high organic removal efficiency with an average DOC removal of 97% from synthetic PTSE.

Sulfide oxidation in fluidized bed bioreactor using nylon support material

A continuous fluidized bed bioreactor (FBBR) with nylon support particles was used to treat synthetic sulfide wastewater at different hydraulic retention time of 25, 50 and 75 min and upflow velocity of 14, 17 and 20 m/hr. The effects of upflow velocity, hydraulic retention time and reactor operation time on sulfide oxidation rate were studied using statistical model. Mixed culture obtained from the activated sludge, taken from tannery effluent treatment plant, was used as a source for microorganisms. The diameter and density of the nylon particles were 2-3 mm and 1140 kg/m3, respectively. Experiments were carried out in the reactor at a temperature of (30 +/- 2) degrees C, at a fixed bed height of 16 cm after the formation of biofilm on the surface of support particles. Biofilm thickness reached (42 +/- 3) microm after 15 days from reactor start-up. The sulfide oxidation, sulfate and sulfur formation is examined at all hydraulic retention times and upflow velocities. The results indicated that almost 90%-92% sulfide oxidation was achieved at all hydraulic retention times. Statistical model could explain 94% of the variability and analysis of variance showed that upflow velocity and hydraulic retention time slightly affected the sulfide oxidation rate. The highest sulfide oxidation of 92% with 70% sulfur was obtained at hydraulic retention time of 75 min and upflow velocity of 14 m/hr.

Properties improvement of paper mill sludge-based granular activated carbon fillers for fluidized-bed bioreactor by bentonite (Na) added and acid washing

Properties improvement of paper mill sludge (PMS) based granular activated carbon fillers for fluidized-bed bioreactor (FBBR) was investigated in this study. Bentonite (Na) powders were blended in the dewatered paper mill sludge powders to strengthen the abrasion resistance strength of the fillers. Different acid washing treatments were studied to produce FBBR fillers with optimum performance. The results indicated that granulation was easy and the abrasion resistance strength of the fillers increased by 15% with 8 wt% of bentonite (Na) added. Acid washing treatment prior to activation had a better effect on the removal of Fe than post-activation acid washing treatment. HCl was the most appropriate acid during the acid washing treatment. The optimum acid washing treatment was carried out prior to activation with 2M HCl soaking for 6h. After acid washing treatment, the fillers with grain density of 1170 kg/m(3), specific surface area of 176 m(2)/g were obtained.

Evaluation of an integrated sponge--granular activated carbon fluidized bed bioreactor for treating primary treated sewage effluent

An integrated fluidized bed bioreactor (iFBBR) was designed to incorporate an aerobic sponge FBBR (ASB-FBBR) into an anoxic granular activated carbon FBBR (GAC-FBBR). This iFBBR was operated with and without adding a new starch based flocculant (NSBF) to treat synthetic primary treated sewage effluent (PTSE). The NSBF contains starch based cationic flocculants and trace nutrients. The results indicate that the iFBBR with NSBF addition could remove more than 93% dissolved organic carbon (DOC), 61% total nitrogen (T-N) and 60% total phosphorus (T-P) at just a very short hydraulic retention time of 50 min. The optimum frequency of adding NSBF to the iFFBR is four times per day. As a pretreatment to microfiltration, the iFFBR could increase 5L/m(2)h of critical flux thus reducing the membrane fouling. In addition, better microbial activity was also observed with high DO consumption (>66%) and specific oxygen uptake rate (>35 mg O(2)/g VSS h).