Monday, January 03, 2005

Efficiency of Aeration System

Efficiency of Aeration System

The efficiency of aeration systems can be measured in different ways. Different aeration system have different efficiency. The exact efficiency of an aeration system is very dependent on the circumstances under which it is measured such as liquid depth, density of diffuser, energy level in the tank, etc. Below is a table of the efficiency of various aeration system adapted to give values in kilowatt-hour per kilogram of oxygen adapted from the table give by Environmental Dynamics In. (Energy Consumption and Typical Performance of Various Types of Aeration Equipment)

Aeration SystemkWh/kg
Mechanical Aeration Systems
Brush aerators surface aeration0.47-0.66
Slow speed surface0.47-0.55
High speed splash surface aeration0.51-0.66
Induced surface aeration1.10-1.64
Combination Systems
Submerged turbine0.66-1.10
Jets (pumps with compressors)0.47-0.82
Diffused Aeration, Coarse Bubble
Static tubes0.47-0.82
Wide band grid0.47-0.66
Misc. coarse bubble0.47-0.82
Diffused Aeration, Fine Pore
Ceramic disc or ceramic dome grid0.23-0.33
Flexible membrane disc0.23-0.41
Advanced Technology membrane0.14

Aerobic wastewater treatment

Aerobic wastewater treatment uses microorganism to feed on waste in the water and convert them to carbon dioxide and water. To keep the process going, the wastewater need to be aerated with oxygen. There are many types of aerators used for this purpose, but all of them involve huge input of energy. Wouldn't it be great if one can have an aerator that can add oxygen to the wastewater without great "input of energy"? What is this "Zero Energy Input" Waterwheel Aerator all about?

I know this "Zero Energy Input" thing will raise some eyebrows! Essential, what it aim to do is to make the energy intensive water aeration more efficient. What I am refering to is a waterwheel aerator using the EXISTING surplus kinetic energy present in wastewater treatment systems to power the aerator to squeeze more oxygen into the wastewater. Thus there is no need for expensive input of energy. Keep a watch on this blog as I will elaborate on this later and also present the results of an investigation which shows that this does work.

Saturday, January 01, 2005

Aeration and aerators

What is aeration?

Aeration is the process by which the area of contact between water and air is increased, either by natural or mechanical means, resulting in air being suspended in water.

Purpose of aeration

One of the pollutants of water are organic matters. The reason why organic matters are considered water pollutants is that microorganism feed on them, and in the process used up the dissolved oxygen needed for aquatic life. If the organic matters are in sufficient quantity, this can lead to nearly all the dissolved oxygen being used up, aquatic life killed, and to anaerobic conditions in which anaerobic microorganism produces hydrogen sulfite and other odorous constitutents are produced.

The purpose of aeration of water is the improvement of their physical and chemical characteristics, the removal or reduction of objectioanl taste and odor and precipitation of inorganic contaminants such as iron and manganese. In water treatment, the purpose of aeration to to ensure continued aerobic conditions for the microorganism to degrade the organic matters.

Types of aerators

Waterfall aerators which uses spray nozzles, cascades or multiple trays

Mechanical aerators which employ motor driven impellers or combination air-injection devices

Surface spray or vertical pump aerator which have a submersible motor which rotates an impeller to pump surface water into the air as a spray. A vertical pump aerator consists of a motor with an impeller (propeller) attached to its shaft. The motor is suspended below a float with a center opening and the impeller jets water into the air at low velocity.

A pump-sprayer aerator employs a centrifugal pump to spray water at high velocity through holes in a manifold and into the air.

Paddle wheel aerator uses paddles mounted on a rotating shaft. A paddle wheel aerator splashes water into the air as the paddle wheel rotates

Propeller aspirator pump. The propeller-aspirator-pump aerator has a high velocity, uncased impeller at the end of a hollow shaft and housing. In operation, air flows down the shaft by the venturi principle and is released into the water in fine bubbles

Diffusion or bubble aerators which bubble compressed air through water. They may be divided into fine pore and coarse bubble aerator. Fine bubble aerators have high OTR (Oxygen Transfer Rate) and high efficiency (oxygen transfered per unit energy per unit time).

Membrane diffuser, a fairly recent technology, operate with low maintenance.