Oily wastes are a significant problem for wastewater treatment, affecting the environment and human health. They are generated from various industrial processes, such as oil-refining and the food industry, which produce waste that contains harmful organic compounds.
Various methods have been developed to treat oily wastes, including biological, chemical, physical and mechanical. However, these systems are prone to operational difficulties, high operating costs and the release of secondary pollutants.
Physical Methods
Oily wastewater generated during the refining process of petroleum is a common problem in the petroleum industry. The environmentally-acceptable disposal of this waste is a significant challenge.
Various physical methods have been developed for oil waste treatment Orange County NY. These include advanced oxidation techniques, coagulation/flocculation, adsorption, centrifugal equipment, ultrafiltration and deep bed filtration, membrane separation technology, and combined technologies.
A ceramic membrane prepared an effective cross-flow microfiltration (MF) process with a 50 nm pore size for oily wastewater treatment under different pressures and initial oil concentrations. The permeate flux was influenced by the transmembrane pressure, the pore size, the flow rate, and the backwashing time. The MF membrane exhibited higher than 99% oil rejection with a TOC removal efficiency of 92% at an operating temperature of 25 deg C and a transmembrane pressure of 138 kPa.
Another effective MF process for oily wastewater was prepared by MnO2 bi-layer composite dynamic membranes containing Kaolin and KMnO4 at a low oil concentration of 0.1 g/L at a transmembrane pressure of 40 kPa. The oil concentration affected the steady permeate flux, but the variation characteristics were not prominent.
Biological Methods
The biological treatment uses microorganisms to remove organic substances and stabilize hazardous pollutants in oily wastewater. However, biological treatments still have a few limitations despite their great potential.
Various chemicals in petrochemical wastes, including aromatic and polycyclic compounds, limit their degradation by microbes. Moreover, BOD removal is difficult in wastewater with a high concentration of these pollutants.
Systems for biological wastewater treatment were created to deal with these issues. They include anaerobic and aerobic digestion, or integrated system with both methods.
Biological processes are used to reduce dissolved and colloidal matter in wastewater before discharge or for the oxidation of lipids to make them less harmful. Typically, they are followed by a separation process, such as flotation or coagulation. Coagulation and flocculation are processes that separate oily solutions by reducing their electrostatic repulsion, through which they tend to destabilize and aggregate into large flocs. These flocs can then be isolated from the solution through precipitation.
Mechanical Methods
Oily wastewater is highly toxic and carcinogenic water with an extensive range of organic pollutants, high levels of nutrients like phosphorus and nitrogen, salt and phenolic compounds. It poses a severe threat to the health of humans and aquatic ecosystems.
Various methods are currently used to treat oily wastewater, including adsorption, centrifuge and bioremediation in an anaerobic environment. However, these methods have several limitations, such as operational costs, the release of secondary pollutants and treatment efficiency.
Coagulation/flocculation is an excellent method to remove oil from wastewater and is considered cost-effective and environmentally friendly. The process starts with destabilizing the colloidal particles by adding appropriate coagulants, destabilizing the electrostatic interactions between the oily particles in the solution and leading to their aggregation into flocs.
This process involves several different coagulants, such as ferric chloride and alum. It is essential to choose the coagulant dose based on the required COD reduction at the end of the treatment.
Chemical Methods
There are a variety of chemical methods for oily wastewater treatment. Adsorption treatments can remove organic compounds and heavy metals from oily wastewater. They can be performed using various adsorbents, such as sawdust, peat, and wool. Powdered activated carbon (PAC) is also a common adsorbent.
The adsorption method is a simple process that can efficiently remove COD and BOD from oily wastewater. It is a relatively low-cost, environmentally friendly and sustainable process.
In addition to adsorption, coagulation/flocculation can destabilize and entrap colloidal particles. These processes are particularly effective when the COD and BOD concentrations are high and are often the best way to remove suspended solids from the water. The most commonly used coagulants are inorganic salts, such as ferric chloride and alum. These act through charge neutralization and bridging, allowing the destabilization of colloidal particles.