Innovations & Ideas
Art of Engineering
From our Partners
Sewage Disinfection - Disinfection Methods
These articles are available in the standard RSS format for publication on your website:
Quantity comparison of disinfection methods
By Dr. Boris Menin
This publication (reference) is one of the few attempts (and far, far from being complete) comparison of electro-physical methods for decontamination of wastewater in terms of specific energy costs for existing publications in the press. The author is grateful for criticism.
Comparing the cost of various methods of sewage treatment is a difficult task, especially when comparing costs in different countries, taking into account population density, level of industrialization and specialization of agricultural imports and exports, output growth, low or high levels of purification, the requirements of existing regulations and laws.
The data for boiling and
alternative powered-consumption methods
of disinfection of waste waters
To estimate the energy required to boil 1 liter (l kg) of water, water temperature is raised 80ºC (from 20ºC to 100ºC) with a biomass stove of 12% efficiency.
(1 kg•80ºC•1.0 kcal/(kg*ºC)•4.19 kJ/kcal)/0.12 = 2,793 kJ/kg water 
For disinfection assume, the water is held at boiling for one minute (as recommended by WHO 1993)), with a stove useful heat output of 1 kW per kg of water held on boil. This energy consumption equals:
1 kW (= 1000 J/sec) / 0.12 • 60 sec = 0.5MJ/kg water 
So the estimated total fuel thermal energy to disinfect water by boiling over a biomass cook stove is:
2.8 MJ +0.5MJ=3.3 MJ/kg water = 920 kWh/m³ 
Ozonation equipment includes air preparation equipment; an ozone generator, contactor, destruction unit; and instrumentation and controls. The capital costs of ozonation systems are relatively high. Operation and maintenance are relatively complex. Electricity represents 26 to 43 percent of total operating and maintenance costs for small systems. Below is an example produced by Mitsubishi Electric.
R & D Process Diagram
The ozonation process at the Chubu Treatment Plant
( Mitsubishi Electric)
Ultra - Violet Light (UV)
The UV units for water treatment consist of a specialized low pressure mercury vapor lamp that produces ultraviolet radiation at 254 nm, or medium pressure UV lamps that produce a polychromatic output from 200 nm to visible and infra-red energy. The optimal wavelengths for disinfection are close to 260nm. Medium Pressure lamps are approximately 12% efficient, whilst Amalgam low pressure lamps can be up to 40% efficient. The UV lamp never contacts the water, it is either housed in a quartz glass sleeve inside the water chamber or mounted external to the water which flows through the transparent UV tube. It is mounted so that water can pass through a flow chamber, and UV rays are admitted and absorbed into the stream. In addition, it is required the installation of a 5 micron pre-filter before all UV disinfection equipment.
(((100 W * 60sec)/5 kg water) /0.33)/(1 – 0.12) = 4,130 J/kg ≈ 1 kWh/m³ 
Comparing equations (3) and (4) suggests that the UV treatment, in terms of primary energy use, is on the order of thousands times more efficient than boiling over biomass.
Main components of ultrasonic systems are:
Radiofrequency (RF) power is a physical method of electromagnetic energy input that heats a product uniformly throughout its volume leaving no chemical residues. The process operates with electrical power that generates a rapidly oscillating electric field between 2 parallel electrodes (RF cavity) where the material to be processed is placed. Dipole and induced dipole molecules in the material continuously align and reorient themselves to the changing electric field, causing friction that converts to heat. In an overall 2-step process, electrical power is first converted to RF power, which is in turn converted into thermal power. Energy-use efficiency for the overall process depends on both power conversion steps.
Electro-Hydraulic Effect (EHE)
Apparatus comprises a container having an inlet and an outlet, through which liquid to be disinfected flows in use; at least one pair of non-sacrificial electrodes. These electrodes being positioned in the container so that liquid flowing through the container is in contact with said electrodes; high voltage electrical capacitors and/or equipment for applying a steady-state electric voltage in the kilovolt range across said electrodes so as to create a voltage gradient between electrodes; the voltage gradient being such that an arc is not struck between electrodes but a voltage gradient of at least one volt is passed through the membrane of each cell, contained in liquid, that causes an electric breakdown of the cell membrane and hence results in destruction of the cell itself.
Light-Hydraulic Effect (LHE)
In generally, apparatus comprises a chamber – “light hydraulic crusher” or “disintegrator”, a closed volume of which is filled with sewage water wherein the light impulse from the laser source is focused with a help of a lenses system. Two hydro-seals of a coil type, create a continuous liquid flow. Besides, they are intended to suppress the shock wave and eliminate the pressure difference and shocks between the chamber and the reservoirs with sewage and disinfected water. It is known that dissolved gases or those formed in the liquid can be released there, thus damping the LH-shocks and reducing the effectiveness of the shock wave action in the chamber during the discharges. A receiver connected to the chamber cavity via a brake channel is positioned in the upper position of the chamber for continuous withdrawal of said gases. Brake channel bends also fully suppress the shock damping in said chamber. The drain cock of the receiver allows to discharge periodically the accumulating gas to the outside.
Creation date : 08/10/2009 @ 11:23
Reactions to this article