**4.4 Anaerobic membrane bioreactors (An-MBR)**

An-MBR can be simply defined as a biological treatment process operated without oxygen and using a membrane to provide solid–liquid separation. The advantages offered by this process over conventional anaerobic systems and aerobic MBR are widely recognized [12].

Saline wastewaters are known for their negative impact on the performance of the biological treatment units. Sodium chloride is widely used, not only for cooking and to melt snow and ice, but also in a wide variety of food industries including food canning, seafood processing, milk processing, etc. In particular, the operation of the seafood processing industry leads to the generation of wastewaters with high soluble and colloidal pollutants and a high concentration of N and SS. For these effluents, the application of conventional biological treatment is not efficient. It was reported that the efficiency could be enhanced by reducing the sodium toxicity with compatible solutes that can increase the sludge activity. Moreover, the anaerobic membrane bioreactor reduces the COD concentration in the wastewater [14].

## **4.5 Anaerobic filter (AF)**

AF consists of a fixed bed biological reactor with one or more series of filtration chambers. This technology relies on the entrapment of the particles in the wastewater on the filter media and the subsequent degradation of the organic matter by the active biomass attached to the surface of the filter media [15]. As the anaerobic biomass should grow on the filter media, 6–9-month start-up period is required for AF to attain the full treatment capacity. The filter can be inoculated with anaerobic bacteria to reduce the start-up time, and the flow should be gradually increased [13, 16].

### **4.6 Blanket/anaerobic filter**

Hybrid UASB/AF systems combine aspects of the UASB process with aspects of the AF process. Influent wastewater and recirculated effluent are distributed across the bioreactor cross section and flow upward through granular and flocculent sludge blankets where anaerobic treatment occurs. The effluent from the sludge blanket zone enters a section of media similar to that used in AF systems where gas-liquid-solids separation occurs. Treated effluent then exits the media section and is collected for discharge from the bioreactor. Gas is collected under the bioreactor cover and is transported to storage and/or use. The hybrid UASB/AF process primarily uses suspended biomass, and process loadings are similar to those used with the UASB process. The solids removal system is similar to that used with the UASB process [8].

A research study on the treatment of wastewater generated from vegetable processing was conducted. In this project, an anaerobic filter, a fluidized bed reactor, and an up-flow anaerobic sludge blanket reactor associated with an anaerobic filter were designed, constructed, and tested [5]. For the anaerobic filter, the removal

efficiency for COD was reported to exceed 80% for HRT of 16 h, at temperatures ranging from 20 to 31°C. The FBAR was operated at HRT of 2 h with mean COD removal efficiency of 63%. The UASB/AF achieved mean COD removal efficiency of 80% at HRT of 6 h [17].
