Jeonghwan Kim

Domestic Wastewater Treatment as a Net Energy Producer–Can This be Achieved?

In seeking greater sustainability in water resources management, wastewater is now being considered more as a resource than as a waste-a resource for water, for plant nutrients, and for energy. Energy, the primary focus of this article, can be obtained from wastewaters organic as well as from its thermal content. Also, using wastewaters nitrogen and P nutrients for plant fertilization, rather than wasting them, helps offset the high energy cost of producing synthetic fertilizers. Microbial fuel cells offer potential for direct biological conversion of wastewaters organic materials into electricity, although significant improvements are needed for this process to be competitive with anaerobic biological conversion of wastewater organics into biogas, a renewable fuel used in electricity generation. Newer membrane processes coupled with complete anaerobic treatment of wastewater offer the potential for wastewater treatment to become a net generator of energy, rather than the large energy consumer that it is today.

The use of nanoparticles in polymeric and ceramic membrane structures: review of manufacturing procedures and performance improvement for water treatment.

Membrane separations are powerful tools for various applications, including wastewater treatment and the removal of contaminants from drinking water. The performance of membranes is mainly limited by material properties. Recently, successful attempts have been made to add nanoparticles or nanotubes to polymers in membrane synthesis, with particle sizes ranging from 4 nm up to 100 nm. Ceramic membranes have been fabricated with catalytic nanoparticles for synergistic effects on the membrane performance. Breakthrough effects that have been reported in the field of water and wastewater treatment include fouling mitigation, improvement of permeate quality and flux enhancement. Nanomaterials that have been used include titania, alumina, silica, silver and many others. This paper reviews the role of engineered nanomaterials in (pressure driven) membrane technology for water treatment, to be applied in drinking water production and wastewater recycling. Benefits and drawbacks are described, which should be taken into account in further studies on potential risks related to release of nanoparticles into the environment.

Anaerobic Fluidized Bed Membrane Bioreactor for Wastewater Treatment

Anaerobic membrane bioreactors have potential for energy-efficient treatment of domestic and other wastewaters, membrane fouling being a major hurdle to application. It was found that fouling can be controlled if membranes are placed directly in contact with the granular activated carbon (GAC) in an anaerobic fluidized bed bioreactor (AFMBR) used here for post-treatment of effluent from another anaerobic reactor treating dilute wastewater. A 120-d continuous-feed evaluation was conducted using this two-stage anaerobic treatment system operated at 35 °C and fed a synthetic wastewater with chemical oxygen demand (COD) averaging 513 mg/L. The first-stage was a similar fluidized-bed bioreactor without membranes (AFBR), operated at 2.0-2.8 h hydraulic retention time (HRT), and was followed by the above AFMBR, operating at 2.2 h HRT. Successful membrane cleaning was practiced twice. After the second cleaning and membrane flux set at 10 L/m(2)/h, transmembrane pressure increased linearly from 0.075 to only 0.1 bar during the final 40 d of operation. COD removals were 88% and 87% in the respective reactors and 99% overall, with permeate COD of 7 ± 4 mg/L. Total energy required for fluidization for both reactors combined was 0.058 kWh/m(3), which could be satisfied by using only 30% of the gaseous methane energy produced. That of the AFMBR alone was 0.028 kWh/m(3), which is significantly less than reported for other submerged membrane bioreactors with gas sparging for fouling control.

Effect of nanoparticle aggregation at low concentrations of TiO2 on the hydrophilicity, morphology, and fouling resistance of PES–TiO2 membranes

This paper reports the fabrication and characterization of polyethersulfone-TiO(2) (PES-TiO(2)) nanoparticle composite membranes made from synthesis casting solution consisting of various compositions of polymer solvents (DMF and EtOH) and TiO(2) additive. The results also revealed that the membrane permeation and rejection rates, pore size, and porosity were dependent on the TiO(2) and EtOH concentrations. Nanoparticles were characterized by zeta potential measurements, TEM observations, and measurement of particle size distributions. Zeta potential measurements in aqueous solution demonstrated that the TiO(2) particles size is dominated by electric double layer interactions. Addition of EtOH promotes the increase of the clusters size as consequence of a double effect: reduction of the dielectric constant of solution and the depletion of the suspension field determined by the action of the polymer chains. The observed effects as result of EtOH addition and increase of TiO(2) concentration were similar: both procedures provoked an increase of macrovoid dimensions. The modified membranes by TiO(2) incorporation showed a structural change from a sponge-like to a finger-like structure. Strong correlations were observed between the hydrophilicity and the permeability of manufactured membranes. The formation mechanism of TiO(2)-blended membranes was altered, in a similar way, as result of EtOH at different contents of nanoparticles. Fouling resistance of modified membranes was significantly improved showing that EtOH addition is a suitable procedure for the membrane performance improvement. The rejection potential of membranes is hardly affected by the nanoparticles and EtOH incorporation into the polymeric solution.

Anaerobic treatment of municipal wastewater with a staged anaerobic fluidized membrane bioreactor (SAF-MBR) system

A laboratory-scale staged anaerobic fluidized membrane bioreactor (SAF-MBR) system was used to treat a municipal wastewater primary-clarifier effluent. It was operated continuously for 192 days at 6-11 L/m(2)/h flux and trans-membrane pressure generally of 0.1 bar or less with no fouling control except the scouring effect of the fluidized granular activated carbon on membrane surfaces. With a total hydraulic retention time of 2.3h at 25°C, the average effluent chemical oxygen demand and biochemical oxygen demand concentrations of 25 and 7 mg/L yielded corresponding removals of 84% and 92%, respectively. Also, near complete removal of suspended solids was obtained. Biosolids production, representing 5% of the COD removed, equaled 0.049 g VSS/g BOD(5) removed, far less than the case with comparable aerobic processes. The electrical energy required for the operation of the SAF-MBR system, 0.047 kW h/m(3), could be more than satisfied by using the methane produced.

Pilot-scale temperate-climate treatment of domestic wastewater with a staged anaerobic fluidized membrane bioreactor (SAF-MBR).

A pilot-scale staged anaerobic fluidized membrane bioreactor (SAF-MBR) was operated continuously for 485 days, without chemical cleaning of membranes, treating primary-settled domestic wastewater with wastewater temperature between 8 and 30°C and total hydraulic retention time (HRT) between 4.6 and 6.8h. Average chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) removals averaged 81% and 85%, respectively, during the first winter at 8-15°C before full acclimation had occurred. However, subsequently when fully acclimated, summer and winter COD removals of 94% and 90% and BOD5 removals of 98% and 90%, respectively, were obtained with average effluent COD never higher than 23 mg/L nor BOD5 higher than 9 mg/L. Operational energy requirement of 0.23 kW h/m(3) could be met with primary and secondary methane production, and could be reduced further through hydraulic change. Biosolids production in all seasons averaged 0.051 g volatile suspended solids per g COD removed.

Doping of polyethersulfone nanofiltration membranes: antifouling effect observed at ultralow concentrations of TiO2 nanoparticles

Doping of nanofiltration membranes with TiO2 nanoparticles was studied in the ultralow concentration range, in the absence of photocatalysis. Blended polyethersulfone/TiO2 flat-sheet membranes were manufactured and investigated in terms of pure water flux, permeability, fouling resistance and solute rejection. The membranes were synthesized at four different polymer concentrations by the phase inversion method, using 1-methyl-2-pyrrolidone (NMP) and deionized water as solvent and coagulant, respectively. The influence of TiO2 addition was investigated in an unusually low concentration interval (0.035–0.375 wt%). The membrane morphology was studied by determining particle size distributions of TiO2 to explore the effect of nanoparticle aggregation. Furthermore, membranes were characterized by hydrophilicity (contact angle), morphology (SEM), porosity, mechanical strength (bursting pressure) and thermal analysis (TGA). Membrane fouling was studied with humic acids as model organic foulants. Overall, a remarkable improvement in the permeability was observed with the addition of ultralow amounts of nanoparticles to the polymer. The optimum permeability was found to be as low as 0.085 wt%, using a constant rejection of dyes as the boundary condition. It was shown that rejection of solutes is not negatively influenced by the increase in permeability. In addition, the resistance against membrane fouling was found to be above 12% for the TiO2 blended membranes.

Anaerobic treatment of low-strength wastewater: A comparison between single and staged anaerobic fluidized bed membrane bioreactors

Performance of a single anaerobic fluidized membrane bioreactor (AFMBR) was compared with that of a staged anaerobic fluidized membrane bioreactor system (SAF-MBR) that consisted of an anaerobic fluidized bed bioreactor (AFBR) followed by an AFMBR. Both systems were fed with an equal COD mixture (200mg/L) of acetate and propionate at 25°C. COD removals of 93-96% were obtained by both systems, independent of the hydraulic retention times (HRT) of 2-4h. Over more than 200d of continuous operation, trans-membrane pressure (TMP) in both systems was less than 0.2bar without significant membrane fouling as a result of the scouring of membrane surfaces by the moving granular activated carbon particles. Results of bulk liquid suspended solids, extracellular polymeric substances (EPS), and soluble microbial products (SMP) analyses also revealed no significant differences between the two systems, indicating the single AFMBR is an effective alternative to the SAF-MBR system.

Effect of temperature on the treatment of domestic wastewater with a staged anaerobic fluidized membrane bioreactor

A laboratory staged anaerobic fluidized membrane bioreactor (SAF-MBR) system was applied to the treatment of primary clarifier effluent from a domestic wastewater treatment plant with temperature decreasing from 25 to 10 °C. At all temperatures and with a total hydraulic retention time of 2.3 h, overall chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) removals were 89% and 94% or higher, with permeate COD and BOD5 of 30 and 7 mg/L or lower, respectively. No noticeable negative effects of low temperature on organic removal were found, although a slight increase to 3 mg/L in volatile fatty acids concentrations in the effluent was observed. Biosolids production was 0.01-0.03 kg volatile suspended solids/kg COD, which is far less than that with aerobic processes. Although the rate of trans-membrane pressure at the membrane flux of 9 L/m(2)/h increased as temperature decreased, the SAF-MBR was operated for longer than 200 d before chemical cleaning was needed. Electrical energy potential from combustion of the total methane production (gaseous and dissolved) was more than that required for system operation.

Low energy single-staged anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for wastewater treatment

An aluminum dioxide (Al2O3) ceramic membrane was used in a single-stage anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for low-strength wastewater treatment. The AFCMBR was operated continuously for 395days at 25°C using a synthetic wastewater having a chemical oxygen demand (COD) averaging 260mg/L. A membrane net flux as high as 14.5-17L/m2h was achieved with only periodic maintenance cleaning, obtained by adding 25mg/L of sodium hypochlorite solution. No adverse effect of the maintenance cleaning on organic removal was observed. An average SCOD in the membrane permeate of 23mg/L was achieved with a 1h hydraulic retention time (HRT). Biosolids production averaged 0.014±0.007gVSS/gCOD removed. The estimated electrical energy required to operate the AFCMBR system was 0.039kWh/m3, which is only about 17% of the electrical energy that could be generated with the methane produced.