Anaerobic biological processes
CSTR (Continuous Stirred Tank Reactor):
A CSTR is a fully mixed reactor that operates in the absence of oxygen. Uniform mixing is achieved through several side-entry or top-entry agitators. Compared to high-rate reactors, this process operates at lower volumetric organic loading rates—ranging from 1 to 5 kg COD/m³·d—and can be utilized even with lower or fluctuating wastewater temperatures. This robust process also offers the advantage of being suitable for wastewater with high concentrations of suspended and dissolved solids, as it operates using a suspended flocculent sludge. Furthermore, because these reactors have a larger footprint than anaerobic high-rate reactors, the roof area can be used as an integrated biogas storage unit, thereby reducing investment costs for downstream biogas handling.
Consequently, the CSTR is ideally suited for industrial sectors that generate lower-temperature wastewater and have sufficient space available on their production site.
UASB (Upflow Anaerobic Sludge Blanket) Reactor:
This type of anaerobic high-rate reactor has been used since the 1980s to treat wastewater with high organic loads.
The wastewater to be treated is distributed evenly via several inlet lines at the bottom of the reactor, which keeps the granulated biomass—characterized by its high settling velocity—in a suspended state. This dense biomass enables the rapid and efficient conversion of organic matter into biogas.
Near the top of the tank, three-phase separators are installed to separate the pre-treated wastewater, the granulated biomass, and the biogas from one another.
The continuous retention of solids within the reactor, achieved through this process, allows for a higher volumetric loading rate of 8 to 9 kg COD/m³·d at wastewater temperatures between 35 and 39 °C. The biogas produced can be treated and used for purposes such as heating the feed water for the UASB reactor, or, where feasible, injected into the gas grid.
The UASB reactor is therefore ideally suited for production facilities with limited space. Although the initial investment costs are higher, they are recouped within a few years through savings in operating costs—specifically regarding energy, aeration, and excess sludge management. With over 20 UASB reactors currently in operation, CUSS is your trusted partner for the construction and operation of high-rate anaerobic reactors. A further advantage for our clients is that the granular biomass required for operation can be supplied anywhere in the world.
EGSB (Expanded Granular Sludge Bed) Reactor:
The EGSB reactor is an anaerobic biological treatment process and an advanced development of the UASB reactor.
This high-rate reactor is used to remove high organic loads from wastewater. Due to its increased upward flow velocity and tall design, it creates an expanded sludge bed, which facilitates more intensive and prolonged contact between the granular biomass and the wastewater being treated.
These reactors, which can reach heights of up to 20 meters, operate at high volumetric loading rates of 20 kg COD/m³·d.
The slender, vertical design significantly reduces the space required for the wastewater treatment plant—an ideal solution for our clients who wish to reserve their limited space on the production site for their core business, while simultaneously ensuring compliance with sometimes stringent environmental standards.
