1. Field
This invention pertains to methods to reduce chemical oxygen demand of waters and industrial wastewater effluents containing starch, milk, whey, and other similar behaving organic components. In particular it pertains to a method for sulfurous acid/lime alkalinization pre-treatment precipitation and coagulation for sequential filtration of waters and industrial wastewaters containing starch, milk, whey, and other similar acting organic components to condition and remove a number of chemicals/pharmaceuticals and heavy metals before treated filtrate is land applied or undergoes further biological reduction for open stream discharge.
As used herein, the term chemical oxygen demand is defined as the amount of chemical and organic pollutants found in waters consuming oxygen, making COD a useful measure of water quality. It is expressed in milligrams per liter (mg/L) also referred to as ppm (parts per million), which indicates the mass of oxygen consumed per liter of solution; see Wikipedia, article on Chemical Oxygen Demand.
2. State of the Art
Various methods have been used to treat and dispose of industrial waste effluents high in chemical oxygen demand. These industrial waste waters are complex solutions and often are colloidal, making them difficult to separate for disposal. As used herein, a colloid is a substance microscopically dispersed throughout waters. The dispersed-phase particles have a diameter of between approximately 1 and 1000 nanometers normally visible with the use of an ultramicroscopic or an electron microscope. The dispersed-phase particles are affected largely by the surface chemistry present in the colloid. Some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color.
Colloidal solutions (also called colloidal suspensions) are the subject of interface and colloid science. When particles are dispersed in liquid, most of them will carry surface charge. The surface charge will attract ions of opposite charge to form a Stern layer where the ions are strongly bound and a diffuse region where they are less firmly associated as shown in FIG. 1. The zeta potential is the electric potential in the inter-facial double layer (DL) at the location of the slipping plane versus a point in the bulk fluid away from the interface. In other words, zeta potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle.
Because the size of the dispersed phase may be difficult to measure, and because colloids have the appearance of solutions, colloids are sometimes identified and characterized by their physical-chemical and transport properties. For example, if a colloid consists of a solid phase dispersed in a liquid, the solid particles will not diffuse through a membrane, whereas with a true solution the dissolved ions or molecules will diffuse through a membrane. Because of the size exclusion, the colloidal particles are unable to pass through the pores of an ultra filtration membrane with a size smaller than their own dimension. The smaller the size of the pore of the ultra filtration membrane, the lower the concentration of the dispersed colloidal particles remaining in the ultra filtered liquid. The exact value of the concentration of a truly dissolved species will thus depend on the experimental conditions applied to separate it from the colloidal particles also dispersed in the liquid.
Many industrial processing wastes, such as starches, milk, and whey are hydro-colloids and have different strength COD. For example, milk and whey processing wastes typically have a COD of ˜2000 mg/l, whereas potato processing wastes typically have a COD of ˜4,000 to 60,000 mg/L. A hydrocolloid is a colloid system wherein the colloid particles are hydrophilic polymers dispersed in water. A hydrocolloid has colloid particles spread throughout water. These hydrocolloids are usually separated using coagulation and flocculation.
Coagulation is the destabilization of colloids by neutralizing the forces that keep them apart as shown in FIG. 2. Cationic coagulants provide positive electric charges to reduce the negative charge (zeta potential) of the colloids; whereas anionic coagulants provide negative electric charges to reduce the positive charge (zeta potential). As a result, the particles collide to form larger particles (flocs). Jar tests adding coagulants with different cationic strengths are taken to determine the best dosages for coagulation and not overdose the coagulants as this can cause a complete charge reversal and re-stabilize the colloid complex.
Flocculation is the action of polymers and other substances to form bridges between the flocs and bind the particles into large agglomerates or clumps, Generally, polymers are most often used as flocculants. Once suspended particles are formed with polymers they agglomerate into larger particles and can usually be removed from the liquid by sedimentation, media filtration, straining or floatation. These particles generally are gelatinous and thereby more difficult to dewater.
Still other industrial wastewater processing components form chemical precipitates with chemicals such as lime, alum, and ferric chloride.
Other COD reduction methods include aeration, bio-degradation, land application, and ponding evaporation and infiltration. These COD reduction methods have differing costs, advantages and disadvantages
The treatment method described below provides an inexpensive chemical treatment method using sulfurous acid/lime alkalinization precipitation and coagulation for sequential filtration of industrial wastewaters containing starch, milk, whey, and other similar acting organic components to condition, agglomerate and reduce suspended and dissolved solids, COD, total nitrogen, and total phosphorous in industrial effluents.