Wastewater treatment technology is key in maintaining environmental sustainability. Whatever kind of water treatment technology for domestic and industrial waste that is built must be operated and maintained by the local community. So the processing technology chosen should correspond to the ability of the technology in question.
A variety of techniques to eliminate waste water treatment pollutant materials have been tried and developed over the years. Processing techniques have been developed waste water is generally divided into three treatment methods :
1. processing in physics
2. chemical processing
3. processing of biologically
For a particular type of waste water, the three processing methods can be applied individually or in combination.
Deposition of suspended material that is not easily done by applying soluble electrolyte having the opposite charge to the charge koloidnya colloid charge neutralization that occurs, so that eventually can be deposited. Provision for heavy metals and phosphorus compounds is done by applying a solution of alkali (eg lime) to form metal-metal hydroxide sludge or precipitate hydroxyapatite. Precipitated metal will be more stable if the pH of water> 10.5 and for hydroxyapatite at pH> 9.5. Specifically for hexavalent chromium, chromium hydroxide is precipitated as before [Cr (OH) 3], first reduced to trivalent chromium by applying reducing agents (FeSO4, SO2, or Na2S2O5).
Coagulation and flocculation
Provision for toxic organic substances such as phenol and cyanide at low concentrations can be done with mengoksidasinya with chlorine (Cl 2), calcium permanganate, aeration, ozone hydrogen peroxide.
Basically we can obtain high efficiency in chemical processing, but the cost will be expensive because it requires processing chemicals.
Processing of biologically
All biodegradable waste water can be treated biologically. As a secondary treatment, biological treatment process is seen as the most inexpensive and efficient. In recent decades has developed various methods of biological treatment with any modification.
Basically, a biological treatment reactor can be divided into two types, namely:
1. Suspended growth reactor (suspended growth reactor);
2. Attached growth reactor (attached growth reactor).
In the suspended growth reactor, the microorganisms grow and develop in a state of suspension. Activated sludge process is widely known place in the reactor of this type. Activated sludge process continues to evolve with various modifications, such as: oxidation ditch and a contact-stabilization. Compared with conventional activated sludge process, oxidation ditch has several advantages, namely BOD reduction efficiency can reach 85% -90% (compared to 80% -85%) and less sludge generated. In addition to higher efficiency (90% -95%), contact stabilization has the advantage of the other, the total hydraulic detention time is shorter (4-6 hours). Contact-stabilization process can also be set aside through the process of absorption of suspended BOD in the tank so it is not necessary contacts suspended BOD removal with preliminary treatment.
Oxidation ponds and the lagoon, either aerated or not, are also included in the suspended growth reactor types. For a tropical climate like Indonesia, hydraulic detention time for 12-18 days in the oxidation ponds and aerated in a lagoon that is not enough to achieve the effluent quality that can meet the standards set. In the aerated lagoon with enough detention time 3-5 days.
In the attached growth reactor, the microorganisms grow on media support by forming a film layer to attach himself. Various modifications have been developed over the years, among others :
1. trickling filter
2. biological discs
3. submerged filter
4. fludisasi reactor
The whole of this modification can result in decreased efficiency of BOD of about 80% -90%.
In terms of the environment in which the ongoing process of biological decomposition, this process can be divided into two types:
A. Aerobic process, which takes place in the presence of oxygen;
2. Anaerobic process, which took place in the absence of oxygen.
If the wastewater BOD does not exceed 400 mg / l, aerobic processes can still be considered more economical than anaerobic. At higher BOD of 4000 mg / l, anaerobic processes become more economical
Processing In Physics
In general, prior to further processing of waste water, it is desirable that the suspended material is large and easy-settle or float materials aside first. Screening (screening) is an efficient and inexpensive way to set aside a large suspended material. Material is easily suspended sediment can be easily set aside by the deposition process. The main design parameters for the deposition process is the speed of the particles settle and hydraulic detention time in the precipitating bath.
Flotation process widely used to eliminate the floating materials such as oils and fats in order not to interfere with subsequent processing. Flotation can also be used as a way of allowance for suspended materials (clarification) or sludge thickening, sludge (sludge thickening) to provide air flow to the upper (air flotation).
Filtration processes in wastewater treatment, usually carried to preempt the adsorption or reverse osmosis process it, will be implemented to eliminate as many of the particles suspended in water so as not to disrupt the process of adsorption or clog the membrane used in the process of osmosis.
Adsorption process, usually with activated carbon, made to set aside aromatic compounds (eg phenol) and other dissolved organic compounds, especially if you want to reuse the wastewater.
Membrane technologies (reverse osmosis) is usually applied to small processing units, especially if the treatment is intended to reuse the treated water. Installation and operation costs are very expensive.
The Chemical Processing
Chemical waste water treatment is usually performed to remove particles that are not easily precipitated (colloidal), heavy metals, phosphorus compounds, and toxic organic substances; by putting certain chemicals are required. Allowance for these materials in principle take place through changes in the properties of these materials, which can be precipitated from not be easily deposited (coagulation-flocculation), either with or without oxidation-reduction reactions, and also takes place as a result of the oxidation reaction.