Low strength wastewater such as municipal sewage is treated using an anaerobic digester. In some examples, a wastewater stream is separated into a solids rich portion and a solids lean portion. The solids lean portion is treated, for example to remove nitrogen. The solids rich portion is treated in an anaerobic digester, preferably with influent or recuperative thickening. In another example, the wastewater stream is fed to an anaerobic digester and solid-liquid separation stages downstream of the digester return active bacteria and undigested organics to the digester. Both cases may use a process train comprising treatment in an anoxic tank followed by a nitritation tank with a portion of the effluent from the nitritation tank recirculated to the anoxic tank to provide nitritation and denitritation.

Disclosed is a method for preparing the same. The method for preparing a carrier including ammonium oxidizing bacteria immobilized therein includes: preparing a PVA-alginate mixed solution containing PVA mixed with alginate; adding sludge containing ammonium oxidizing bacteria and sodium bicarbonate (NaHCO.sub.3) to the PVA-alginate mixed solution to obtain a foaming-beading solution; and dropping the foaming-beading solution to a saturated boric acid solution to obtain beads including sludge immobilized therein, wherein sodium bicarbonate (NaHCO.sub.3) is decomposed to produce carbon dioxide (CO.sub.2) which is discharged to the exterior of the beads to form pores in the beads, when the foaming-beading solution is dropped to the saturated boric acid solution to obtain beads including sludge immobilized therein.

An apparatus and method for selecting and retaining solids in an activated sludge process for the improving wastewater treatment using screens. The screens can be used to separate and retain solids based on size or compressibility. The screens are used to separate and select for slow growing organisms, faster settling organisms, or materials added to absorb, treat or remove constituents in the activated sludge process.

A process for converting ammonium (NH.sub.4.sup.+) of a mainstream of a wastewater plant to dinitrogen gas (N.sub.2), including the consecutive steps of i.) removing biodegradable carbon compounds in the mainstream, ii.) converting ammonium (NH.sub.4.sup.+) in the mainstream to nitrite (NO.sub.2.sup.−) in an aerated biological process containing ammonium oxidizing bacteria (AOB) in a nitration vessel (133a-133d); and iii.) denitrifying the resulting stream from step ii.) to dinitrogen gas in an anammox vessel (200). Growth of nitrite oxidizing bacteria (NOB) in step ii.) is prevented by periodically subjecting the bacteria in said nitration vessel (133a-133d) to water suppressing growth of nitrite oxidizing bacteria (NOB).

A treatment system of the present invention generally includes a plurality of high surface area sheets anchored to a fixed base. The sheets are generally vertically oriented although able to flex and sway independently. Substantially all regions of substantially all sheets are aerated. The sheets are constructed of an open weave substrate that allows the diffusion of gas, nutrients and food, while protecting and serving as an attachment site for a variety of microbial colonies in both anoxic and aerobic zones. In use a system of the present invention is inserted into a wastewater reservoir, and aerated, for treatment of the wastewater.

A treatment system of the present invention generally includes a floating support structure having an upper flotation assembly, a base assembly that secures the bottom edges of a plurality of low density sheets, and vertical frame members that connect the upper flotation assembly to the base assembly. The sheets are generally vertically oriented although able to flex and sway independently. Substantially all regions of substantially all sheets are aerated. The sheets are constructed of an open weave substrate that allows the diffusion of gas, nutrients and food, while protecting and serving as an attachment site for a variety of microbial colonies in both anoxic and aerobic zones. In use a system of the present invention is inserted into a wastewater reservoir, and aerated, for treatment of the wastewater.

[Problem] A carrier for retaining anammox bacteria, an anammox bacteria-adhered particle, and a wastewater treatment apparatus are provided that can remarkably reduce the start-up period for obtaining a nitrogen removal speed of 1 kg-N/m.sup.3/day. [Solution] A carrier for retaining anammox bacteria includes carbon particles. The carbon particles are desirably graphite particles, particularly isotropic graphite particles. The carbon particles desirably have a zeta potential of −35 mV to 0 mV and an average particle size of 2 μm to 1000 μm.

A system and method of treating wastewater having at least one undesirable biological species is provided. In accordance with embodiments, a wastewater treatment system is provided comprising a main biological treatment train including at least one first unit operation configured to perform an anaerobic ammonium oxidation process, and at least one subsystem configured to increase a concentration of anammox bacteria in the at least one first unit operation, the treatment system arranged to reduce the concentration of total nitrogen in the wastewater.

A wastewater treatment system and a wastewater treatment process, fluidly combining a one or more SBR (sequencing batch reactor) module/s, in which nitrification and denitrification of the wastewater are performed in sequences and one or more MBR (membrane bioreactor) module/s.

There are provided processes for treating wastewater. The processes can comprise treating a mixture comprising the wastewater and an activated sludge, in a single reactor, with an electric current having a density of less than about 55 A/m.sup.2, by means of at least one anode and at least one cathode that define therebetween an electrical zone for treating the mixture; exposing the mixture to an intermittent ON/OFF electrical exposure mode to the electric current in which an OFF period of time is about 1 to about 10 times longer than an ON period of time; and maintaining an adequate oxidation-reduction potential in the single reactor. Such processes allow for substantial removal of carbon, nitrogen and phosphorus from the wastewater in the single reactor of various forms and for obtaining another mixture comprising a treated wastewater and solids.