V. Mavrov

Hybrid flotation-membrane filtration process for the removal of heavy metal ions from wastewater

A promising process for the removal of heavy metal ions from aqueous solutions involves bonding the metals firstly to a special bonding agent and then separating the loaded bonding agents from the wastewater stream by separation processes. For the separation stage, a new hybrid process of flotation and membrane separation has been developed in this work by integrating specially designed submerged microfiltration modules directly into a flotation reactor. This made it possible to combine the advantages of both flotation and membrane separation while overcoming the limitations. The feasibility of this hybrid process was proven using powdered synthetic zeolites as bonding agents. Stable fluxes of up to 80l m(-2)h(-1) were achieved with the ceramic flat-sheet multi-channel membranes applied at low transmembrane pressure (<100 mbar). The process was applied in lab-scale to treat wastewater from the electronics industry. All toxic metals in question, namely copper, nickel and zinc, were reduced from initial concentrations of 474, 3.3 and 167mg x l(-1), respectively, to below 0.05 mg x l(-1), consistently meeting the discharge limits.

Study of a hybrid process combining ozonation and membrane filtration — filtration of model solutions

Abstract A hybrid process, consisting of ozonation and membrane filtration, was studied for the treatment of surface water or low-contaminated process wastewater. The main focus of this study centres on tests to determine the effect of ozone on membrane fouling during microfiltration and ultrafiltration. In this work, ceramic membranes with pore sizes in the range of 0.2 μm to a cut-off of 1 kD underwent lab-scale tests using model bentonite and humic acid solutions. Results showed that, by adding ozone during microfiltration and ultrafiltration of the humic acid solutions, membrane fouling for all membranes could be greatly reduced, thus obviating the need to backflush or clean the membranes. As for the bentonite solutions however, membrane fouling, which was caused by deposits of suspended inorganic substances, was not affected to any great extent by the addition of ozone. Microporous membranes with a pore size in the range of 10–50 nm proved to be the best possible option for this hybrid process.

Study of new integrated processes combining adsorption, membrane separation and flotation for heavy metal removal from wastewater

Abstract A new treatment process aimed at water and metal reuse was developed for the selective separation of heavy metals from wastewater to reduce costs and mitigate the environmental impact of wastewater pollutants. The process was divided into the following three stages: firstly, heavy metal bonding by a bonding agent, secondly, wastewater filtration to separate the loaded bonding agent by two variants: crossflow microfiltration for low-contaminated wastewater or a hybrid process combining flotation and submerged microfiltration for highly contaminated wastewater, and th irdly, bonding agent regeneration. In this work, synthetic zeolite P, selected as a bonding agent, was characterised and the possibilities for the separation of the zeolite loaded with metal are presented.

Characteristics and application of new ceramic nanofiltration membranes

In this study, the characteristic and filtration behaviour of a newly developed ceramic nanofiltration membrane was studied and compared to other commercial ceramic nanofiltration membranes currently available. It could be shown that it was possible to produce a ceramic membrane with separation properties in the nanofiltration range and with permeability rates clearly superior to that of polymer nanofiltration membranes. The ceramic membrane was used in tests involving the treatment of textile wastewater, alkaline solutions from bottle washing machines and pickling bath solutions.

Recycling of spent process water in the food industry by an integrated process of biological treatment and membrane separation

Abstract An integrated membrane filtration process was developed to produce water of drinking quality out of polluted process water from small and medium-sized enterprises in the food and beverage industries. It comprised a membrane-supported bioreactor and a combined nanofiltration/UV disinfection stage. The process was implemented in demonstration scale (up to 1.5 m 3 /h) at a fruit juice production plant. In the bioreactor, COD removal rates >95% were achieved. After the second treatment step, the chemical and bacteriological parameters of the treated water met the limits of the German Drinking Water Act (DWA). After authorisation procedure by the responsible authorities, the technology tested was granted approval for water reuse in the food industry. The influence of biological process parameters on the flux of the bioreactor membranes was investigated as well as backflushing and CIP cleaning procedures. In the second treatment step membrane permeability depending on different operating conditions was investigated. The treated water can be re-used for various purposes, e.g. boiler make-up water, cooling water. Amortisation periods of less than 3 years are possible, depending on the water re-use potential.

Concepts for the treatment of spent process water in the food and beverage industries

In the food and beverage industries, spent process water streams containing very different levels of contamination are combined and routed to the mixing and equalizing tank where problems in biological wastewater treatment occur. It could be shown that the treatment of the partial streams for different applications resulted in major benefits while problems with biological wastewater treatment could be minimized or even eliminated. For example, tests showed that the product could be recovered from the highly contaminated pre-rinsing water in production plants and water of drinking quality could be produced from the mixed spent process water. The process steps to achieve this, can be simplified as follows: a) for product recovery: integrated microfiltration and oil skimming; for water reuse: 1) pretreatment to remove suspended solids, droplets and the bulk amount of dissolved organic impurities as well as to reject the microorganisms (membrane biology); 2) Membrane filtration to remove residual dissolved inorganic and organic impurities (two-stage nanofiltration); 3) UV disinfection to ensure that the treated water will ultimately meet the legal bacteriological standards for drinking water.

Treatment of spent process water from a fruit juice company for purposes of reuse: hybrid process concept and on-site test operation of a pilot plant

Abstract In order to treat spent process water from companies of the food and beverage industries up to drinking water quality, a process concept was developed consisting of the following two treatment steps: (1) biological COD reduction using a membrane bioreactor (MBR) in which the active biomass as well as other particulate matter were completely retained by means of immersed hollow-fibre MF membranes, and (2) subsequent reduction of bacterial germs, residual organics as well as of inorganic constituent compounds by means of downstream two-stage nanofiltration with integrated UV disinfection. This hybrid process was tested by operating a pilot plant (capacity 100 l/h) for 6 months at a fruit juice company in order to treat spent process water (COD: 2,500–6,500 mg/l; electrical conductivity: 2,300–4,700 μS/cm) from the on-site mixing and equalising tank. The process under study proved to be technically feasible and reliable. The treated water was partially desalted and fulfilled both the chemical and bacteriological standards required by the German Drinking Water Act. Therefore, it can be reused, for example, as cooling or boiler make-up water as well as for pasteurisation, preparation of conveyor belt lubricants and bottle washing. Based on the results obtained, a preliminary evaluation was conducted to determine the investment and operating costs required for implementation of the tested hybrid process.

Membrane processes for water reuse in the food industry

By using low-contaminated process water from the food industry, a new water treatment technology, capable of producing water which can be reused (e.g. water for cleaning and cooling, boiler feed water) was developed. The treated water fulfills the requirements specified in drinking water regulations. At present, this water treatment technology is undergoing authorisation procedure.

Treatment of low-contaminated waste water from the food industry to produce water of drinking quality for reuse

Abstract The treatment of low-contaminated waste water from the meat processing industry was studied with the objective of producing water of drinking quality for reuse. A demonstration plant with a capacity of up to 2 m3/h was built based on our experiments to compare different treatment processes for the removal of suspended particles, dissolved inorganics, undissolved and dissolved organics and micro-organisms contained in the waste water and which exceed the limit for drinking water. The demonstration plant consists of water pretreatment (sedimentation with fat skimming, cartridge filtration and UV disinfection), nanofiltration and post-treatment (UV oxidation and UV disinfection). The experimental results from an operating period of over 4 months showed that treated water with drinking water quality, according to the German drinking water regulations, can be produced. The applied waste water technology is now undergoing authorization procedure with the German authorities.

Desalination of surface water to industrial water with lower impact on the environment: Part 4: Treatment of effluents from water desalination stages for reuse and balance of the new technological concept for water desalination

Abstract Within the framework of our new technological concept for the desalination of surface water to industrial water, the production of a mixed acid and a mixed base by electrodialysis with bipolar membranes (EDBM) from effluents was one main objective of the study. After optimized pretreatment, reverse osmosis (RO) or electrodialysis reversal (EDR) concentrates and regenerates from cation and anion exchangers can be used as feed solutions for the production of an acid and a base by EDBM. The products obtained fulfill the requirements for ion exchanger regeneration chemicals. A material balance of the new technological concept for typical river water shows that—in comparison with conventional methods for the production of desalinated water—there is less raw water consumption, less wastewater is generated and fewer commercial chemicals are needed.