Systems for removal of ions from aqueous fluids are provided. In certain embodiments, the present disclosure provides a system comprising a mixing chamber for mixing calcium ions and an aqueous fluid that contains one or more oxyanions; a reactor that receives the aqueous fluid from the mixing chamber, and contains an aluminum metal, where an initial amount of the aluminum metal contained in the reactor is based at least on a calculated corrosion rate, wherein the aluminum metal releases aluminum ions that react with the one or more oxyanions in the aqueous fluid to form a precipitate comprising one or more ettringites; an agitation device to agitate the aqueous fluid and the aluminum metal, one or more measurement devices connected to the reactor, and a controller for operating the agitation device based at least on measurements taken by the measurement devices.

The removal of oxoanions from an aqueous stream having a concentration of a metal cation and a concentration of an oxoanion that varies over time may involve continuously monitoring the concentration of the metal cation and the concentration of the oxoanion to provide a current metal cation concentration and a current oxoanion concentration. A metal cation source and an aluminum reagent may be added to the aqueous stream based on the measured current metal cation concentration and the current oxoanion concentration. The amount of the metal cation source and the aluminum reagent added to the stream may be effective to reduce the concentration of the oxoanion in the aqueous stream below a target threshold.

A method of desulfating seawater includes adding a produced water to a sulfated seawater, forming a first precipitate, separating the first precipitate from the sulfated seawater, measuring the sulfate ion concentration of the desulfated seawater, adding a precipitating agent to the sulfated seawater, and separating a second precipitate from the sulfated seawater. Another method of desulfating seawater includes determining concentrations of sulfates in a sulfated seawater and a precipitating agent in a produced water, adding the produced water to the sulfated seawater based on the determined concentrations of sulfates in the sulfated seawater and the precipitating agent in the produced water, forming a first precipitate, separating the first precipitate from the sulfated seawater, measuring the sulfate ion concentration of the desulfated seawater, adding a precipitating agent to a sulfated seawater, and separating a second precipitate from the sulfated seawater.

A method and system of providing seawater into a subterranean formation, including adding chloride salt having a metal cation to the seawater (having sulfate), precipitating sulfate salt (of the metal cation and sulfate), removing the sulfate salt as precipitated to give treated seawater having less sulfate than the seawater, and injecting the treated seawater into the subterranean formation.

Methods of controlling hydrogen sulfide concentration of a biogas occupying an anaerobic membrane bioreactor (AnMBR) containing a submerged membrane are disclosed herein. Methods of controlling dissolved sulfide concentration of a mixed liquor within the AnMBR are disclosed. The methods include directing wastewater containing sulfur and a chemical oxygen demand (COD) to an AnMBR, withdrawing at least a fraction of the biogas from the AnMBR, directing a pre-determined amount of the withdrawn biogas to a scrubber, directing a remainder of the withdrawn biogas to a gas distributor, and directing the scrubbed biogas to the AnMBR. Systems for treating wastewater having sulfur and COD are disclosed. The systems include an AnMBR, a scouring gas closed loop, a scrubber, and a control mechanism for directing biogas to the scrubber and to a gas distributor. Methods of retrofitting a system for treating wastewater having sulfur and COD are disclosed.

A method of treating wastewater includes supplying, to a stirring tank, wastewater which includes sulfate ions and is stored in a collecting tank, supplying a solvent to the stirring tank into which the wastewater is supplied, forming sulfuric acid crystals by stirring the wastewater and the solvent supplied to the stirring tank, and supplying, to a separation tank, a mixture solution of the sulfuric acid crystals and treated water which is the wastewater from which the sulfuric acid crystals have been precipitated, and separating the sulfuric acid crystals and the treated water from each other in the separation tank, wherein the solvent is hydrophilic but has low affinity for the sulfate ions.

Precipitation or scaling may occur when combining produced water from multiple sources, such as when one produced water contains dissolved calcium ions and another produced water contains dissolved sulfate anions. The tendency toward precipitation or scaling may be decreased by treating the produced water containing dissolved sulfate anions. Such methods may comprise: providing a first produced water comprising dissolved sulfate anions; treating the first produced water with a metal salt capable of forming an insoluble metal sulfate, thereby forming a metal sulfate precipitate and a treated produced water; separating the metal sulfate precipitate from the treated produced water; and after separating the metal sulfate precipitate, mixing the treated produced water with at least one second produced water to obtain a mixed produced water, the at least one second produced water containing dissolved calcium ions, and the mixed produced water having a saturation ratio for calcium sulfate of less than 1.