The wastewater treatment processes required for industrial wastewater are diverse because of the variety in their contaminants. However, basic wastewater treatment steps for both municipal and industrial wastewater are almost always the same.
Step 1: Screening, first to remove large objects and second to remove grit.
Step 2: Primary clarification to seperate solid organic matter.
Step 3: Aeration to promote conversion of NH3 into NO3 and oxygen for bacteria growth
Step 1: Wastewater screening
Screening is used to remove solid waste from wastewater. This can cause damage to other equipment, reduce the efficiency of the entire system, or cause waterways contamination.
Halpin & Hayward LTD has a range of screens. The Climber Screen uses a smooth-running, endless track system that employs a gear-driven cleaning rake. It can carry screenings from a submerged barrack to a discharge chute for their removal. The rake can easily tackle large obstructions. To clear large objects, the rake simply disconnects from the bar rack until it is removed in a subsequent pass.
Step 2: Primary Separation and Clarification
Clarification is a process that removes suspended solids from wastewater and produces a clear liquid effluent which can be used for downstream treatment.
There are two types: primary and secondary wastewater clarification.
Primary clarification: Prevents solids in wastewater before biological treatment.
Secondary clarification: After biological treatment, the activated sludge is rapidly returned to the aeration tanks.
The solids separation process is widely used in water treatment plants. It is critical for the preparation of water and wastewater and the pretreatment of various types of wastewater.
A lot of industrial wastewaters contain large amounts of suspended solids. These could be pulp fibers from paper manufacturing wastes, metal particles from iron and steel processing operations, coke fines of power plants, oil, grease from food processing, oil refining operations or clay particulates that have been emitted from the plant runoff. A solids removal step is often included in industrial wastewater treatment plants. The solids separation process is also used in secondary treatment to separate and thicken biological substances at the secondary treatment stage, remove suspended solids via filtration at end of plant and remove water from wet solids or sludge.
The removal of hydrocarbons from wastewater can be a challenge if it contains large amounts. Oil has a lower density than water. Therefore, if the wastewater is not emulsified it can be floated in separate removal stages or in a dual purpose vessel that allows sedimentation. As an example, the refinery industry uses a rectangular clarifier that has a surface skimmer to extract oil and a bottom-rake to remove solids. This design is an API separator.
Air flotation can be used to increase oil removal in cases where the density differential is too low to separate oil from oil-wetted substances. Air bubbles attach to the contaminant particles and increase the apparent density difference. Dissolved Air flotation (DAF), is a technique that introduces air to a side stream, or recycle stream at elevated pressures to create a supersaturated stream. This stream is introduced to the waste stream at atmospheric pressure and then the air is released in small bubbles. These bubbles attach themselves to the contaminants in the waste stream, decreasing their effective densities and aiding in their separation.
Step 3: aeration
The activated sludge is only possible through aeration. There are many methods of aeration:
High-rate Aeration: High rate aeration is used in the log growth phase. Recirculation is used to replenish excess food in the biomass population. This design results in a significant amount of biochemical oxygen demand (or BOD) from the effluent. The oxidation process is not completed.
Conventional aeration is the most commonly used activated sludge type by industry and municipalities. It operates in an endogenous phase to produce acceptable effluent levels in BOD (Body Oxygen Demand) and total suspended solids(TSS). Conventional aeration is considered a “middle-of-the-road” method because it has higher capital and operating costs than the high rate process but lower than the extended aeration plant.
Extended aeration: Extended aeration plants work in the endogenous phase, but require longer periods of oxygenation to lower effluent BOD levels. This results in higher capital and operating expenses (i.e. larger basins and greater air). Extended aeration, in conjunction with a lower BOD, produces a relatively high level of suspended solids effluent when the optimum natural settling levels are exceeded.
Tapered aeration/step aeration: The head of a plug flow basin receives waste in its most concentrated form. This is where metabolism and oxygen need are highest. The rate at which the waste is being disposed of through the basin decreases (or the respiration rate), as a result of the advanced stage in oxidation.
Contact a representative to learn more about Halpin & Hayward LTD in Dublin industrial wastewater treatment services.