Electrical coagulation technology is a physiochemical treatment for the treatment of water: waste water, process water, mine water, etc., to remove suspended solids, emulsified hydrocarbons and heavy metal ions (including radionuclides). It also removes/destroys most pathogens present at the same time. The technology was originally developed in 1906 to treat bilge water from ships to remove oils, but was abandoned at the time due to the absence of international agreement regulating discharges at sea.
Electrical coagulation process
Electrical coagulation cells consist of multiple pairs of metal parallel plate electrodes separated by a few millimetres and arranged so that the water to be treated flows through the plates at a moderate rate, a direct current voltage is applied across the plates. Provided that this current density is sufficiently high to cause electrolysis of the water a number of processes take place simultaneously and may be summarised as:
- Electronic charge destabilisation of suspended colloids causing them to separate out and coagulate and of emulsions/microemulsions causing them to break and the hydrocarbons to coalesce.
- Release of reactive oxygen, hydroxyl and other radicals which react with dissolved organic and ammoniacal compounds oxidising them and causing heavy metals to separate from solution as oxides/hydroxides.
- Production of large amounts of fine gas bubbles which promotes the flotation of coagulated solids and coalesced hydrocarbons.
The electrical coagulation process has been proven to produce smaller amounts of denser, less hydrated flocs than conventional chemical flocculation and also to successfully treat waste water containing pollutants where conventional techniques have failed.
Benefits and economics
Benefits of electrical coagulation water treatment include:
- Electrical coagulation is a proven technology to treat and clean-up process water streams for re-use/discharge either standalone or integrated into an existing treatment works to improve the discharges. It may also advantageously be used as a pre-treatment to protect other water treatment technologies including: reverse osmosis, ion exchange, membrane filters, etc.
- Compared with other technologies, electrical coagulation is a low energy, continuous flow process.
- With modification, the electrical coagulation process may be used to rapidly oxidise, and hence remove, compounds which give rise to high levels of biological and chemical oxygen demands (BOD and COD).
- Heavily contaminated discharges may be treated using one or more stages of electrical coagulation to comply with consent levels for heavy metals, arsenic, hydrocarbons, BOD and COD. A single pass through a Electrical coagulation cell will normally remove better than 90% of contaminants, depending upon flow rate, nature of the contaminants and pH, and two passes greater than 99%.
- Electrical coagulation will also remove the majority of biological loading (bacteria, algae, viruses, larvae) in waste water streams in a single pass.
- The electrical coagulation process has a small footprint compared with other waste water treatment systems and may be supplied in ATEX compliant containers for certain oil, gas and chemical industry applications.
- The process is cost effective in use when used to treat water contaminated with high levels of colloids, organic compounds, heavy metals, etc., and can vary from £25.00 per 1m3 down to £2.00 to per 1m3 depending upon pollutants, volumes to be treated and location of operation.
Water treatment applications
Applications for electrical coagulation include:
- Oil platform waste water and slops – removal of emulsified hydrocarbons, clays and heavy metals.
- Oil refineries and distribution depots – removal of emulsified hydrocarbons and dissolved organic compounds from process and groundwater, reduction in biological and chemical oxygen demands (BOD and COD).
- Ships and oil tankers – removal of hydrocarbons, dissolved organic compounds, heavy metals and fish/animal larvae from bilge and ballast water prior to discharge.
- Food and dairy processing plant – removal/recovery of emulsified fats, oils and greases, reduction in biological and chemical oxygen demands (BOD and COD).
- Drinking water purification - removal of arsenic and heavy metals.
- Mine water and precious metal extraction tailings – recovery of gold, platinum, etc., removal of heavy metals, sulphides, arsenic.
- Contaminated perched water and groundwater.
Electrical coagulation systems
Brownfiled and its partners have developed electrical coagulation cells and control systems which incorporate a number of innovations that combine to give improved performance over conventional designs:
- The electrical chemistry has been optimised for efficient operation using high currents and low voltages (8 volts maximum selection).
- Uses a unique hydrodynamic design of electrical coagulation cells to optimise water flow through the cells.
- The cells are sealed during operation and the water flow is upwards to remove hydrogen and oxygen bubbles produced to flotation unit and to prevent any floc or sediment build up in the cells.
- The electrical coagulation cell plates are fitted in quick change carrier cartridges to minimise cell downtime during plate replacement.
- Each cell has a separately controlled power supply and the electrical coagulation cells are plumbed in pairs in parallel in each treatment unit so that any one may be completely isolated from the supply for change of a cartridge without halting the treatment process.
- Custom designed air eductors to mix additional gas into the exits from the electrical coagulation cells to further enhance the processes which take place in the flocculation and sedimentation unit.
Biological and chemical oxygen demand reduction
Brownfiled and its partners have developed a modified electrical coagulation process, which will oxidise and substantially reduce concentrations of soluble organic compounds such as surfactants, organic acids and alcohols, sulphides, ammoniacal compounds, etc. These are responsible for the BOD and COD in waste water and process discharges.