Brewery Wastewater Management
Aerobic Wastewater Treatment
Aerobic biological treatment is performed in the presence of oxygen by aerobic microorganisms (principally bacteria) that metabolize the organic matter in the wastewater, thereby producing more microorganisms and inorganic end-products (principally CO2, NH3, and H2O). The bacteria in aerobic systems are generally more tolerant to pH and temperature swings than anaerobic systems. The pH of the system should range from 7.0 to 7.5. Aerobic bacteria are less sensitive to alkaline pH than to acidic pH, and systems operating below pH 6 may encounter problems. Some of the aerobic treatments available to brewers include bioreactors, septic tank, and ponds.
Bioreactors
There are a number of different types of bioreactors that can be used in wastewater treatment from sludge bed/sludge blanket, membrane, moving bed, fluidized bed, inverse fluidized bed, and downflow stationary fixed film bioreactors.
Activated Sludge
The conventional activated sludge process employs an aerobic tank which is an agitated vessel (stirred tank bioreactor) seeded with an inoculum of microbial sludge (usually the recycled portion of active sludge). This complex mixture containing bacteria, fungi, protozoans, and other microorganisms is referred to collectively as the biomass. In this process, the suspension of aerobic microorganisms in the aeration tank, are mixed vigorously by aeration devices which also supply oxygen to the biological suspension. Aeration devices commonly used include submerged diffusers that release compressed air and mechanical surface aerators that introduce air by agitating the liquid surface.
Membrane Bioreactors
A membrane bioreactor (MBR) is a biological wastewater treatment system that incorporates a microfiltration membrane on the discharge to remove virtually all suspended solids, bacteria, and protozoa from wastewater. Membrane bioreactors primarily target BOD and TSS. Membrane filtration involves the flow of water containing pollutants across a membrane.
Sequencing Batch Reactors
Sequencing batch reactors (SBRs) provide a well-established alternative to conventional activated sludge treatment; the biology is the same and only the format varies.
Moving Bed Biofilm Reactor
Moving bed biofilm reactor (MBBR) is a process whereby wastewater is aerated in the presence of micro-organisms, which grow on the surface of solid media. The large surface area of the bio-media provides abundant surface for bacteria to grow and thrive.
Trickling Filter Process. In the trickling filter process, the wastewater is sprayed over the surface of a bed of rough solids (such as gravel, rock, or plastic) and is allowed to “trickle down” through the microorganism-covered media.
Biofiltration Towers. A variation of a trickling filtration process is the biofiltration tower or otherwise known as the biotower. The biotower is packed with plastic or redwood media containing the attached microbial growth.
Septic Tanks
For small breweries with low production and wastewater flows, installation of a relatively simple wastewater treatment system consisting of a settling tank (a septic tank) and with a subsurface drainage discharge area (a leach field) may meet their needs (Figure 25.1). In these systems, solids are allowed to settle in the septic tank, and the effluent is discharged to an adjacent leach field.
Ponds
Ponds are often used by smaller breweries to accomplish biological stabilization (Figure 25.2). The ponds provide an environment for aerobic degradation of wastewater constituents near the surface, coupled with anaerobic degradation by microbes at depth.
Pond Microbiology
A wide variety of microscopic organisms may be found in process wastewaters, though the bacteria are the primary mechanism of biological treatment. As bacteria multiply, the individual cells form porous, fractal structures called floc. A firm, dense floc enhances gravity settling to produce clear effluent. A floc is a type of microbial aggregate that may be contrasted with biofilms and granules, or else considered a specialized type of biofilm. Thus, bacterial growth and floc structure control effluent quality.
Aeration
Aerobic degradation can be accelerated by installing aerators to increase available oxygen and preclude stagnation. Aerated ponds, if properly designed, constructed and managed, can reduce organic, nutrient, and solids loadings and provide good quality effluent fit for irrigation.
Hydraulic Detention Time
Detention times must be long enough for bacteria to reproduce and metabolize the maximum organic waste load entering the pond.
Location and Design
Ponds may be installed where the slope of the land is not too steep to cause problems with their construction and where soils are sufficiently impermeable to retain effluents in the lagoon. Low permeability clay and/ or liners should be used in lagoon construction to minimize effluent leaching to groundwater.
Advantages and Disadvantages
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