Wastewater treatment

How is wastewater treated?

Wastewater treatment can be divided into 3 stages - preliminary treatment, primary treatment, secondary treatment. Preliminary treatment consists of physical screening of large objects. In Primary treatment, the wastewater is held in a separation tank to allow particles to settle to the bottom and grease to float to the top. The solids are drawn off the bottom and skimmed off the top and sent for further treatment as sludge. Secondary treatment is a biological treatment to remove dissolved organic matter from the wastewater. Aerobic microorganisms are allowed to consume the dissolved organic matter. For this purpose, sufficient oxygen have to be provided and this is where aeration comes in. For more details, links to other websites are provided below:

Wastewater Treatment Principles and Regulations

Wastewater Treatment, Water Use

AERATION

BOOKS:

Theory and Practice of Water and Wastewater Treatment

Wastewater Engineering: Treatment and Reuse

Small and Decentraliszed Wastewater Management System

Simplified Wastewater Treatment Plant Operations

Water and Wastewater Calculations Manual

Zero Energy Waterwheel Aerator

Before the non-believers of zero energy devices start bashing this blog, let me explain that the reference to no energy input refers to the claim that one do not supply any energy to this aerator. One uses external existing waste energy to power the aerator. Wastewater in wastewater treatment plant such as oxidation ditch are often in constant motion.

Oxidation ditch
Oxidation ditch
Oxidation ditch
Floating aerator
Note the tremendous amout of turbulance (kinetic energy) in the water stream.

ZERO ENERGY INPUT AERATOR

The device being proposed consists of circular discs fitted with suitable number of paddles. When flowing wastewater pushes against the paddle, the discs rotates. As the discs rotate, wastewater clinging to the surface of the discs are brought up and large surfaces of the wastewater are constantly exposed to the air for the diffusion of oxygen into the water.

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 System	kWh/kg
Mechanical Aeration Systems
Brush aerators surface aeration	0.47-0.66
Slow speed surface	0.47-0.55
High speed splash surface aeration	0.51-0.66
Induced surface aeration	1.10-1.64
Combination Systems
Submerged turbine	0.66-1.10
Jets (pumps with compressors)	0.47-0.82
Diffused Aeration, Coarse Bubble
Static tubes	0.47-0.82
Wide band grid	0.47-0.66
Misc. coarse bubble	0.47-0.82
Diffused Aeration, Fine Pore
Ceramic disc or ceramic dome grid	0.23-0.33
Flexible membrane disc	0.23-0.41
Advanced Technology membrane	0.14

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.

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.