High-Rate Anaerobic Systems UASB & ECSB

The UASB (Upflow Anaerobic Sludge Blanket) process is the most applied anaerobic technology for the biological treatment of high-rate industrial effluents.

UASB use gas/liquid/solids (GLS) separators and overflow weirs in the digester top section to separate biogas and biomass and settle and return biomass to the digester sludge bed.

Typical characteristics of UASB Reactors are:

• Maximum process stability due to controlled external re-circulation flow which is not depending on the influent COD/flow
• Due to the ability  to store gas, a separate biogas holder may not be required
• Phase separators constructed of PP, eliminating risk of corrosion
• No complex or rotating equipment inside the reactor requiring maintenance
• Loading rates are typically in the range of 5 – 15 kg COD/m3 .day

 

The Hydrothane ECSB is a proven high-rate anaerobic system that uses anaerobic bacteria (biomass) to convert organic pollutants or COD (chemical oxygen demand) into biogas in an oxygen-free environment. The system comprises two vessels being the neutralisation tank and the main reactor. The main reactor contains a highly efficient phase separator that retains the sludge as the water passes though to the point of discharge.

Industrial wastewater may require pre-treatment in the form of screening followed by clarification or dissolved air flotation prior to anaerobic treatment for the removal of gross solids and to reduce the concentrations of oil and grease. Some additional wastewater conditioning may also be necessary  to ensure that there are sufficient nutrients and trace metals, and the temperature and pH are within a suitable range.

Biogas is a mixture of gases produced during the anaerobic digestion of organic matter. It is generally composed of 60–65% methane (CH4) and 35–40% carbon dioxide (CO2). Minor constituents are hydrogen sulphide (H2S), nitrogen (N2), hydrogen (H2).

There are many uses for biogas although in industrial applications biogas is most commonly used as an alternate fuel source for boilers and when in sufficient quantities converted to electricity.  When biogas is used as a fuel it must be carefully conditioned to the specification required for its intended use.

A gas flare is always installed to allow biogas to be safely burned off whether biogas is being reused or not and  treatment of biogas  to remove impurities is essential.

Hydroflux supply a range of biogas treatment systems that are engineered to maximise the recovery and utilisation and will comprise:

Biogas collection

Positive displacement blowers will often be required to transfer biogas from the covered anaerobic lagoon at a controlled rate and pressure to downstream equipment

Biogas Chilling

Digester produced biogas is 100% water saturated as as it cools in the lines to the point of reuse, large amounts of water will condense in the piping system . Hydroflux will incorporate the most suitable biogas cooling system into the treatment process

Biogas Treatment

Removal of hydrogen sulphide from biogas is essential to avoid rapid corrosion. Hydroflux offer a range of chemical, media or biological gas scrubbers that will ensure that the biogas is suitably conditioned for reuse.

The Hydrothane ESCB is suitable for the treatment of wastewater from many industries and is ideal for high COD loads in excess of 5 T per day when biogas recovery is most beneficial. Anaerobic treatment will not remove nutrients and a second aerobic stage is necessary for environmental discharge.

Is anaerobic treatment suitable for my application?

There are a number of factors to consider which will determine whether anaerobic digestion of your wastewater is a suitable solution. Firstly an anaerobic treatment plant will not remove BOD to levels that allow discharge to the environment or for reuse, nor will it reduce the levels of nutrients. In saying this however, for high COD loads, anaerobic digestion upstream of an aerobic process such as the Hydroflux SBR, MBR, MBBR will significantly reduce the load on the aerobic process lowering the overall capital and operating costs of the treatment plant whilst having the possibility of generating and reusing biogas.

Anaerobic treatment is best suited to relatively high flows and for economical gas recovery generally over 3-4T of COD a day would be necessary.

How much  space will I need?

Each system is designed to suit the specific characteristics of the wastewater in question however,  the Hydrothane ESCP process is however one of the most compact anaerobic systems available worldwide utilising tall reactors that save on surface area. The reactors can extend up to 20m high.

The main reactor itself is usually sized based on a loading rate of 15-35 Kg COD / m3 / day, thus for a COD load of 3000Kg per day, the diameter of the main reactor could be as little as 5m.

How much biogas will the system generate?

The amount of gas generated depends on a number of factors but of most value is the COD load. As a rule of thumb for every Kg of COD, 0.35m3 of biogas will be generated. This biogas will need to be conditioned for reuse as it will be contaminated with carbon-dioxide (CO2) along with some trace gasses such as hydrogen sulphide (H2S), nitrogen (N2), hydrogen (H2) and oxygen (O2).

Hydroflux can complete all the following works in house which are typically required to construct a wastewater treatment plant.

• Process design, development of PID’s and HAZOPS reviews
• Establishment of the most suitable wastewater treatment plant layout
• Equipment and component selection
• Civil and building designs including preparation of documentation for council or other regulators
• Electrical design and programming
• Project management and site supervision
• Environmental / Occupational health and safety plans and report
• Quality assurance plans
• Earthworks, civil works, building works, mechanical and electrical installation
• Commissioning, training and documentation as required.