Abstract: The invention relates to a process for treating a chromate waste liquid containing an organic acid component. This process includes (a) adding a chromium precipitation accelerating agent containing at least one of a calcium component and a magnesium component, to the chromate waste liquid; and (b) adjusting the chromate waste liquid to having a first pH of 9 or higher, thereby precipitating a chromium component from the chromate waste liquid and thereby reducing a concentration of a dissolved chromium component of the chromate waste liquid.

Abstract: An improved process for the removal of cyanide ion from aqueous dispersions (e.g., aqueous spent cadmium plating solutions or plating rinse water solutions) is provided wherein a source of Fe+2 ion is reacted with a cyanide ion-containing aqueous dispersion at low pH to form a relatively insoluble reaction product complex, whereupon the reaction product is removed by filtration or the like. In preferred practice, the pH of a waste water is adjusted to a level of up to about 2, followed by the addition of ferrous ammonium sulfate.

Abstract: A process is provided to create a treated recycle stream through pre-treatment and solids separation for reuse in animal feeding operations without odors and creates a treated liquid effluent that can be stored for reuse, or can be land applied without odors and is free from pathogens and nutrients. Additionally the methods describe a means of converting animal manure to organic fertilizer and removing nutrients from the liquids to create a feed supplement from biomass. The organic fertilizer is non-leaching and free from pathogens. The entire process is accomplished in a reduced footprint from other treatment processes and allows waste ponds to be removed from service.

Abstract: The present invention provides methods to remove metals from water in a cost effective and efficient manner using an inorganic cross-flow filter.

Abstract: In a waste water treatment apparatus, sludge settled in a settling tank is treated by being introduced (returned) into a return sludge reaction tank having a settling section in its rear portion. Therefore, unreacted chemicals contained in the sludge that has settled in the settling tank can be utilized in the return sludge reaction tank. Therefore, the unreacted chemicals are not discharged as sludge. Accordingly, as compared with the conventional treatment method of discharging a sludge from the settling tank, it is possible to reduce the amount of generated sludge remarkably and consequently, reduce a sludge disposal fee, the use amount of slaked lime, and a running cost such as maintenance cost of a dehydrator.

Abstract: A method and system for removing heavy metals from wastewaters is provided wherein the wastewaters are pre-treated with a polymeric metal removing agent to assist in the removal of the heavy metals. The polymeric metal removing agent promotes the precipitation of large particles which may then be filtered by a high flow rate, low pressure filtration system.

Abstract: A process for the treatment of waste waters containing chemically reducible dissolved organic and inorganic pollutants and suspended mater in particulate or colloidal form. The process comprises of contacting the water with metallic iron or ferrous ions (Fe2+), or mixtures thereof, in the presence of promoter metals, such as Cu, Pd, Pt, Au, Ag, and Ni, or oxides, sulfides and other insoluble compounds of these meals, which catalyze the redox reductions carried out by the iron or ferrous reagents. The production of ferric ions (Fe3+) as a final iron oxidation product allows for the simultaneous coagulation and precipitation of suspended colloidal and particulate solids out of the aqueous phase. In addition to the main reductive reaction scheme, the system performs a multitude of secondary reactions involving the ferrous and ferric ions produced in-situ which allows for the simultaneous removal of specific target pollutants, such as phosphate and hydrogen sulfide.

Abstract: A process for utilizing the material of ammonium-containing effluent which contains further soluble constituents and, possible additional solids, comprising:

Abstract: A method for treating livestock wastewater includes directing screened wastewater to a hydrocyclone/separation tank system. The hydrocyclone directs the wastewater stream in a generally helical fashion to create bubble-particle aggregates. Activating chemicals can be added to the wastewater upstream of the hydrocyclone or within the hydrocyclone itself. The wastewater is channeled from an outlet of the hydrocyclone through a diffuser to a separation tank, where the bubble-particle aggregates are separated as they rise and accumulate on a free liquid surface of the tank. The treated wastewater settles below the bubble-particle aggregate accumulation and is transferred to a reservoir for later use as irrigation water or barn wash water. Salts may also be removed from the wastewater by filtering the wastewater through salt-removing filters before the wastewater is transferred to the reservoir.

Abstract: A process for reducing boron and/or fluoride ion content of water. Feed water is contacted, in the presence of magnesium, with an alkaline hydroxide to produce treated water and a magnesium precipitate containing boron and fluorine. The precipitate is separated from the treated water. The boron content of water is reducible from above about 0.8 mg/L to below about 0.7 mg/L, and the fluoride ion content is reducible from above about 1 mg/L to below about 0.9 mg/L. The magnesium precipitate is optionally used to neutralize pressure oxidized ore slurry or roaster calcine in the context of gold recovery operations.

Abstract: The present invention relates to a process for treating more or less concentrated aqueous effluents, such as processing waters, industrial or urban waste waters, and sludges, in particular sludges derived from these waste waters. The said process comprises at least one step of physical separation of a liquid phase and of a solid phase dispersed in the said liquid phase and at least one addition of chemical conditioning reagents and optionally of antifoaming agents. The process also comprises the injection of carbon dioxide (CO2) into the said aqueous effluents, in an amount which is sufficient to give them a pH of less than 7.8.

Abstract: This invention relates to a process for removing sulphates and calcium from a water stream which includes the steps of: combining the water stream and an amount of amorphous aluminum trihydroxide (Al(OH)3); allowing the formation of ettringite (3CaO.Al2O3.3CaSO4.31/32H2O) as a precipitate; and removing the precipitated ettringite from the water stream.

Abstract: A method of treating animal manure solids comprises contacting the solids with a treatment composition comprising AlCl3.nH2O or Al(NO3)3.mH2O, or the residue of AlCl3.nH2O or Al(NO3)3.mH2O, to form a treated waste product, wherein n is from 0 to 10, and m is from 0 to 12. The treatment amount can be effective to reduce phosphorus solubility in the manure; reduce phosphorus runoff and/or phosphorus leaching from fields fertilized with manure; inhibit ammonia volatilization from the manure; flocculate solids in the manure; reduce pathogens in the manure; increase the nitrogen content in the manure; and/or reduce acid rain and PM-10s associated with the manure.

Abstract: The present invention relates to a method of treating alkaline waste water originating from washing spent oil which has undergone an alkaline treatment with water and which contains organic material. This method can produce water which can be discharged into conventional industrial water treatment facilities or which can be used directly as a base for preparing fertilizers or for preparing an agent for preventing ice formation on road surfaces.

Abstract: A method and apparatus for removing a group of species of metal ions from an aqueous solution to be purified which involves the steps for each species in succession of adjusting the pH of the aqueous solution to a value where hydroxide precipitates of said species in its highest valency state are insoluble, then passing the aqueous solution through an ion state modification cell to raise the valence of the respective species to its highest valency state thus causing the ion specie to form the insoluble hydroxide, then removing the precipitated hydroxide from the aqueous solution by appropriate steps of settling and press filtering. A magnetic field is imposed between the electrodes which improves the efficiency of the ion state modification step.

Abstract: The present invention is directed to a method for removing selenium from a waste stream. The process is a multi-step process that removes selenium from a waste stream in the form of barium selenate and/or barium selenite. In a further step, the barium selenate and/or barium selenite forms a complex precipitate with barium sulfate, which encapsulates the barium selenate and/or barium selenite. The complex precipitate is subsequently removed from the waste stream.

Abstract: The invention relates to a method for purifying protein containing waste water, In which a) a first insoluble material is caused to form in the waste water, b) the mixture obtained in step a) is separated to form pre-purified waste water, c) the pre-purified waste water is treated with aerobic microorganisms and d) the mixture obtained in step c) is separated to form finely purified waste water, and in which step b) and step d) are carried out in the same device. Preferably, steps b) and d) are alternately carried out in the same device.

Abstract: A water soluble copper salt, preferably cupric sulfate pentahydrate, is mixed with water. A small quantity of an acidic flocculant is added to the copper sulfate solution to acidify the water and promote dissolving of the copper sulfate in the water. A 25-50% water solution of an acidic flocculant, with or without a cationic polymeric flocculant aid, is prepared and pumped into a processing vessel or tank. The acidified copper sulfate solution is added to the tank and mixed with the acidic flocculant. The algicide-flocculant solution is transported to a municipal water plant and added to raw water in the clarifier to drop out particulates in the incoming water and control algae in the clarifier.

Abstract: A process for the removal of dissolved metals and/or metalloids from an aqueous medium having a high content of salt wherein the aqueous medium in the presence of manganese (II) ions and an oxidation agent is passed through a particulate carrier material having a specified density, initial average grain size and flow rate, so as to fluidize carrier material particles in the aqueous medium, and whereby the coated material particles thereby formed are separated from the aqueous medium.

Abstract: A method for the removal of copper from waste waters includes providing a solution to be treated, the solution comprising copper; introducing a source of ferric ions and a source of ferrous ions into the solution; and adjusting the pH of the solution to promote formation of a copper-containing ferrite precipitate, whereby the solution is depleted in copper. In instances where the solution contains ferric ions, the method includes introducing a source of ferrous ions into the solution to obtain a solution comprising ferric ions and ferrous ions; and adjusting the pH of the solution to promote formation of a copper-containing ferrite precipitate, whereby the solution is depleted in copper.

Abstract: Modification of phosphoric acid manufacturing provides improved process waters: decontaminated water pH-adjusted to be only slightly acidic, scrubber process water, gypsum stack water, and a composite of the latter two waters. The composite water undergoes two-stage neutralization with clarification, eliminating precipitatable contaminants, in forming the pH-adjusted water, which in turn is useful in forming scrubber process water or gypsum stack water, as needed, Resulting gypsum stacks and rainfall surge ponds, having been made relatively fluoride-free through such processing modification, and preferably also having been lined, supersede previous gypsum stacks and acid gypsum ponds—whether lined or not.

Abstract: A method for removing the oxy-anions of selenium from FGD scrubber purge water. The purge water is contacted with free hydroxyl radicals to effect oxidation of reduced forms of sulfur to sulfate and the destruction of sulfur-nitrogen compounds present in the purge water. The purge water is then subjected to chemical reduction and co-precipitation of selenium with an amount of ferrous ions effective to remove the oxy-anions of selenium in the liquid in less than 30 minutes of reaction time. The resultant ferrous-selenium solids generated are separated and stabilized to elemental selenium in a separate reaction vessel.

Abstract: The present invention provides a crystallization process for removing fluoride from waste water. Fluoride-containing waste water is introduced into a fluidized bed crystallizer provided with a carrier. A water soluble sodium reagent and a water soluble aluminum reagent are added into the fluidized bed crystallizer to form crystallized cryolite (Na3AlF6) onto the carrier. The treated waste water is separated from the fluidized bed crystallizer to obtain a primary treated water. The formed cryolite is in the form of crystals, which contain about less than 10% water, and is very convenient for re-utilization.

Abstract: The present invention relates to an apparatus for removing volatile impurities such as mercury and selenium from a weak acid solution resulting from scrubbing gases created in the production of sulfuric acid by roasting of sulfide concentrates. The apparatus comprises a calcine filtering unit for removing calcine from the weak acid solution, a sodium sulfide mixing unit for precipitating mercury from the weak acid solution, a sodium dithionite mixing unit for precipitating selenium from the weak acid solution, and a mercury-selenium filtering unit for filtering the precipitated mercury and selenium from the weak acid solution. The present invention further relates to a treatment plant utilizing such an apparatus, a process for removing volatile impurities from a weak acid solution, and a selenium cake obtained by utilizing the resent invention.

Abstract: Wastewater streams containing tacky or sticky components and heavy metals, such as photoresist-containing streams from printed-circuit board manufacture and water streams from paint spraying processes, can be detackified and the metals simultaneously removed by addition of a metal salt, such as an iron salt, and a sulfide material. The combination of metal salts and sulfide reacting products produces a detackified metal sulfide sludge that improves the filterability of the wastewater while also removing dissolved metal ions from the wastewater.

Abstract: A method of purifying an aqueous liquid stream is provided, wherein the liquid stream is pressurized and contains proteinaceous materials, such as blood, and suspended solids, comprising the introduction of carbon dioxide into the liquid stream in a manner to reduce the pH of the liquid stream sufficient to cause coagulation ofthe proteinaceous materials. Specifically, it is intended that the pH of the liquid stream is reduced to a level below the isoelectric point of the proteinaceous materials, preferably at a level below pH 4.5. In a preferred method, the liquid stream is moved by a dissolved gas pump, wherein the carbon dioxide is introduced into the dissolved gas pump, and wherein a first portion of the gas is caused to dissolve within the liquid stream, and a second portion of the gas is caused to entrain within the liquid stream in the form of micro-fine bubbles.

Abstract: A method for treating sludge from wastewater purification is described. In the method, a sludge is treated, which contains phosphorus and at least one metal which originates from precipitation chemicals and which is selected among divalent iron and aluminum, the pH of the sludge being adjusted to below 4, preferably below 2, for dissolving the content of the phosphorus and said metal in the sludge; the remaining sludge is separated; the solution relieved of sludge and containing phosphorus and said metal is treated for precipitation of the phosphorus content of the solution as FePO4 at a pH of 2-3; and precipitated FePO4 is separated. The method is characterized in that the solution which remains after separation of FePO4 and which contains said metal from the precipitation chemicals, is recycled to the wastewater purification. The phosphorus content of the solution is precipitated as FePO4 by adding an at least equivalent amount of Fe3−.

Abstract: A process for removing fluoride from wastewater is presented. Calcium (or magnesium), sodium and aluminum reagents are added into a fluidized bed crystallizer to remove most of the fluoride in wastewater. The remaining fluoride is removed by aluminum hydroxide. Alternatively, two fluidized bed crystallizers are used in series to treat the fluoride-containing wastewater: in the first fluidized bed crystallizer, calcium (or magnesium), sodium and aluminum reagents are used to treat the wastewater which contains high concentrations of fluoride, so that the fluoride concentrations thereof are largely reduced. Then, in the second fluidized bed crystallizer, a calcium reagent is added to further remove fluoride therein.

Abstract: The present invention relates to a process for treating more or less concentrated aqueous effluents, such as processing waters, industrial or urban waste waters, and sludges, in particular sludges derived from these waste waters. The said process comprises at least one step of physical separation of a liquid phase and of a solid phase dispersed in the said liquid phase and at least one addition of chemical conditioning reagents and optionally of antifoaming agents. The process also comprises the injection of carbon dioxide (CO2) into the said treated aqueous effluents, in an amount which is sufficient to give them a pH of less than 7.8.

Abstract: The present invention entails a composition and process for treating wastewater. The composition is made up of calcium hydroxide, bauxite, and activated carbon. This composition is mixed and continuously fed into a reactor(s) containing wastewater. The composition facilitates the settling and treating of solids for disposal as well as reducing odors and improving the color and quality of the wastewater to make it suitable for subsequent discharge. Additionally, a polymer can be added to promote flocculation and the further settling of suspended solids. An oxidant, such as chlorine gas, may also be added. In the case of chlorine gas, it reacts with ammonia nitrogen to convert the same to hydrochloric acid, water, and elemental nitrogen. Further, the present invention entails a chemical composition provided for reacting with hydrocarbon compounds and breaking them down so as to render them non-toxic and non-hazardous.

Abstract: A process for removing or stabilizing arsenic and/or selenium from aqueous streams or slurries is provided that includes contacting the streams or slurry with a composition containing lanthanum chloride. The lanthanum chloride composition can optionally contain various lanthanides. The composition can optionally contain ferric or ferrous sulfate. The process is preferably conducted by adjusting the pH of solution to between about 8 or 10, adding 2 moles of lanthanum chloride for every mole of arsenic or selenium ions present in solution, adding 5 to 6 moles ferric or ferrous ions for every mole of arsenic or selenium ions present in solution and adjusting the oxidation potential of the solution to between 200-400 mV for removal of selenium ions and between 100-200 mV for removal of arsenic ions.

Abstract: The invention relates to desalination of Sea water and of brakish water, and removal of harmful CO2 gas in exhaust from combustion apparatuses. The exhaust, rich in carbon dioxide (CO2) is diverted to a process chamber, where Sea water, after being mixed with Ammonia, as a catalyst to weaken the salt molecules, is pumped into the chamber and dispersed at many points near the top, as a fine spray, exposing the salt to the CO2 gas there. The internal bond of the salt molecules (NaCl) are weaker by the Ammonia in the water attaching and pulling on their Cl atom. The CO2 in the chamber is attaching and pulling on the Na atom of the salt molecules and are further reduces the bond, breaking them apart. Two heavy solids are formed, they settle in a clarifier below and are removed. Desalinated Sea water, in large quantities per ton of salt, over flows from the clarifier, for use in communities and for agriculture.

Abstract: An aqueous solution, for example, effluent from an off-gas scrubber, is treated to remove metal and metalloid ions by in situ precipitation of ferrous ions by the addition thereto of a ferrous ion-containing solution, salt or other such ferrous ion-containing source and a hydroxyl-yielding base in the presence of the metals and metalloids. The reaction conditions include a temperature of at least about 60° C., and a pH of from about 6 to about 10.

Abstract: A method of treating an effluent such as acid mine drainage wherein the pH of the effluent is increased by dissolving metallic ions e.g. of zinc into the effluent, and the metallic ions are allowed to react with contaminants, such as sulphates or phosphates in the effluent, to form a metal-contaminant complex which is then precipitated from the effluent.

Abstract: The present invention relates to a process for the treatment of arsenic-containing sludge obtained by adjusting arsenic-containing waste water to a PH of 12 or greater by the addition of a calcium compound and subjecting the waste water to solid-liquid separation, the process comprising the steps of adding a calcium compound to the arsenic-containing sludge slurry obtained by the solid-liquid separation, dewatering the resulting sludge, drying the dewatered sludge, and calcining the dried sludge. According to the present invention, arsenic-containing sludge obtained by treating waste water to precipitate arsenic present therein can be calcined to yield a calcined product which involves no risk of arsenic redissolution when it is dumped. Moreover, there is no possibility that arsenic compounds may be volatilized during calcination.

Abstract: A simple, rapid, efficient and inexpensive process for on-site recycling of wastewater with minimal odor wherein the solid wastes generated by the water treatment process are dewatering on-site by solar energy to water content levels below those required for disposal. All operations, including solar dewatering, are accomplished in a compact unit which may be mobile. The solar dewatering unit includes a drying pan over which a solar collector window arrangement is disposed. In the process, wastewater, a water purifying composition and an oxidizing agent are additively mixed together in a first reactor settling tank and the resulting composition is neutralized to a pH of between 7.5-9.4. The added water purifying composition is then allowed to precipitate wherein it binds to and precipitates heavy metals as well as other impurities. The precipitated purifying composition forms a non-hazardous sludge at the bottom of the tank.

Abstract: The aqueous wash stream of an electrolytic precipitation system treating natural gas liquid (NGL) is maintained at a pH sufficiently basic to decrease the solubility of iron sulfide in the aqueous wash stream.

Abstract: Methods and compositions are disclosed for treating swimming pool waters in order to remove one or more nutrients necessary for algal growth and to accelerate the breakdown of objectionable chloramines within chlorinated pool waters. The target nutrients of preference are those containing phosphorus or nitrogen. Phosphorus nutrients are preferably removed by ion-exchange with finely divided lanthanum carbonate, or by direct precipitation in the pool with liquid lanthanum chloride. Nitrogen nutrients (including, in particular, chloramines) may be removed (possibly with the aid of catalysts and in separate reactors). The same reagents used to scavenge phosphates are useful in this regard, the nitrogen being released from the pool water as a nitrogenous gas. To allow the fine lanthanum carbonates to be conveniently handled in the pool environment, they may be linked to larger carrier particles, such as those of diatomaceous earth, or they may be embedded within porous beads formed from polymers or gels.

Abstract: A process to purify wastewater by chemical oxidation is disclosed. The purification is carried out in a fluidized bed of a suitable particulate carrier upon which the iron(III) compound produced by Fenton's reaction crystallizes or coats, thereby reducing the sludge content of effluent over 50%. In addition, the fluidized bed improves the COD removal by way of thoroughly mixing the wastewater with adding agents.

Abstract: The present invention relates to a method of treatment of acid waste waters or acid drainage waters containing metals comprising ferrous and ferric ions, the method comprising increasing the pH of the acid waste to at least 7.5 by addition of an alkaline reagent under conditions such that ferrous ions are stable with respect to oxidation to ferric ions, to form a precipitate and collecting the precipitate.

Abstract: Disclosed is a method for treating highly concentrated wastewater by electrolysis and oxidization, said method being characterized in that the electrolysis and oxidization are carried out in a fluidized bed of a suitable particulate carrier. The electrolytic reduction efficiency of ferric ions is improved by the fluidized particulate carrier, and thus a high proportion of iron(III) to iron(II) can be sustained in the system. This invention allows extensive purification of wastewater with improved efficiency.

Abstract: The present invention relates to methods for concentrating bacteria from a viscous biological sample. The methods involve adding to the sample a water-soluble, density-lowering agent having a density of 0.7 to 0.9 g/ml and a boiling point greater than 50.degree. C. The invention also relates to methods for concentrating bacteria and free bacterial nucleic acids from a biological sample that involve mixing with the sample a density-lowering agent and a monovalent salt.

Abstract: A flocculant composition includes an aqueous solution of a mixture of titanyl sulfate or titanium tetrachloride with a water-soluble, neutral alkali or alkaline earth metal salt at a titanium to alkali or alkaline earth metal salt ratio calculated as TiO.sub.2 of from 0.25:1 to 0.0002:1 by weight. The flocculant composition may further contain a water soluble iron salt at a titanium to iron ratio calculated as TiO.sub.2 and Fe.sub.2 O.sub.3 of from 1:1 to 40:1 by weight, or a water-soluble zirconium salt at a titanium to zirconium ratio calculated as TiO.sub.2 and ZrO.sub.2 of from 1:1 to 40:1 by weight, or a water soluble aluminum salt at a titanium to aluminum ratio calculated as TiO.sub.2 and Al.sub.2 O.sub.3 of from 1:1 to 40:1 by weight.

Abstract: A balanced water purification composition is provided with a buffer compound, and oxidizer/clarifier compound, and a biocide compound. The composition purifies and clarifies water while maintaining the existing water pH. The composition may also include a filtration aid, an algicide, a calcium releasing source, a chelator, and a sequestering agent.

Abstract: Disclosed is a two-stage high pressure high recovery process utilizing two reverse osmosis membrane systems intended to provide very high overall water recoveries from contaminated inorganic scale-containing water in an economical manner while preventing scale formation on the membrane and prolonging the useful life of the membrane. The first stage of the process involves using a low pressure membrane system to preconcentrate scale compounds while purifying the bulk volume of the scale-containing water (using antiscalants with pH control) and combining the influent water with a recycle stream of concentrate from the second stage membrane process in order to prevent scale formation. This first stage membrane system is followed by a second stage membrane system wherein the concentrate from the first stage membrane system is treated further at higher pressure in order to provide purification of the remaining preconcentrated stream and achieve very high overall water recoveries.

Abstract: An apparatus and method for removing contaminating metal ions and sulfate ions from acidic aqueous solution such as waste mine water which features passing the solution between pairs of electrodes, each pair of electrodes impressed with a voltage selected according to specific ion species and then adding chemical agents to raise the pH and form precipitates of the metal and sulfate ions. A magnetic field is applied during at least the first mixing step. The precipitate is then separated from the water with settling and filtering steps. The clarified solution is treated by reverse osmosis to concentrate the ammonium.

Abstract: A method of treatment of an arsenic sludge obtained from a solid-liquid separation step on arsenic waste water by adjusting the value of pH to 12 or higher by adding a calcium compound is disclosed. The method is characterized by addition of hydrated lime and calcining the sludge.

Abstract: In the method for the humid treatment of effluents containing a compound selected from the group consisting of H.sub.2 SO.sub.4, free SO.sub.2, SO.sub.3.sup.-, or SO.sub.4.sup.= and having a pH lower than 5, the effluents are reacted with a basic compound. Particles selected from the group consisting of CaCO.sub.3.MgCO.sub.3, MgCO.sub.3 and a mixture of these, are used for treating the said effluents, the said particles having a particle size such that at least 95% of the particles selected from the group consisting of CaCO.sub.3.MgCO.sub.3 and MgCO.sub.3 have a particle size smaller than 75 .mu.m. After treatment magnesium sulfate in the form of a solution or brine is recovered.

Abstract: The present invention relates to a process for treating contaminated water to precipitate metals without increasing the total dissolved solids content. In particular, the invention relates to the use of phosphoric acid and calcium hydroxide or calcium oxide to adjust the pH of chromium contaminated groundwater during the treatment process without increasing the total dissolved solids (TDS).

Abstract: A process for treating industrial waste water containing hexavalent chromium (Cr.sup.+6) and other heavy metals is disclosed which comprises reduction of Cr.sup.+6 to trivalent chromium (Cr.sup.+3) and the precipitation thereof with other heavy metals by addition of sulfide ion and ferrous ion to the waste stream at a pH of about 7 to 9 under conditions such that sludge production by the process of the invention is substantially less than that characteristic of prior art processes. Polymers are added to the solution to assist flocculation and clarification of the waste stream. More specifically, the invention comprises adding sulfide ion in a sulfide to hexavalent chromium ratio of about 0.7-2.5:1 and adding ferrous ion in a ferrous to hexavalent chromium ratio of about 0.5-5.0:1. The waste stream pH is preferably maintained in the range of about 7.2 to 7.5.