Wastewater Treatment: Stages and Processes
Wastewater Treatment: An Overview
Wastewater treatment is a crucial process divided into several stages to remove contaminants and make water safe for reuse or discharge. This document outlines the key stages involved.
Pre-treatment
Pre-treatment serves to regulate and measure the flow into the plant, extract large floating solids and sand. This stage uses equipment such as grilles and screens. The plants are designed to treat a specific volume of water. Pretreatment steps include:
- Entry and Elevation of Raw Water: The water reaches a thick shaft where heavier materials are decanted to the bottom.
- Desbasting: Elimination of coarse and fine solids that are poured into tapes and stored in containers to be carried to a landfill.
- Sanding, Degreasing, and Sand and Grease Elevation: Elimination of sand and grease.
Primary Stage
The primary stage removes suspended solids by sedimentation or with coagulant aids or flocculants. Sedimentation ponds and primary clarifiers are used. This process removes 60 to 70% of solids in suspension. Solids deposited on the bottom are removed by rotating blades, and floating elements are removed.
Secondary Stage
The secondary stage aims to remove organic matter and colloidal substances through oxidation followed by sedimentation. This stage involves bacteria that feed on suspended solids, producing CO2 and water degradation, resulting in bacterial biomass that precipitates in the secondary decanter. The secondary decanter has a tranquil flow of water, so bacterial flocs sediment. This sediment is called activated sludge. This is also known as biological treatment. This process degrades organic matter through microorganisms. The treatment has two parts:
- Aerobic Zone: Allows increasing the number of bacteria.
- Anaerobic Zone: (No information provided)
Secondary decanters separate treated water from biological sludge through secondary clarifiers, depositing the mud at the bottom, and the treated water is discharged.
Sludge Treatment
Sludge containing 99% water, bacteria, and organic and inorganic pollutants is treated in different ways (anaerobic digestion, aerobic digestion, composting, chemical conditioning, and physical treatment).
Dehydration of the Sludge
Equipment such as sand beds and filter presses are used. These sludges must be disposed of in an environmentally responsible manner, such as through agricultural land application or incineration.
Tertiary Stage
The objective of the tertiary stage is to remove specific contaminants, such as phosphates from domestic and industrial detergents. The treated water can be used for agricultural purposes, irrigation, or disinfection. Not all plants include this phase.
Industrial Filtration
Industrial filtration involves passing water through a filter to retain solids. Different types of filters are used depending on the industrial application. Wastewater treatment processes in refinery catalytic cracking and hydrotreating form acid waters, which are treated by a steam stripping process before being sent to the treatment plant to remove traces of sulfur and ammonia. The stages are:
- Primary Treatment: Separating oil and solids in suspension.
- Secondary Treatment: Removes emulsified hydrocarbons.
- Tertiary Treatment: Removes dissolved hydrocarbons.
- Quaternary Treatment: Applied to waters that will be reused in the process.