ultrasonic_water_waste_water_and_algae_treatment

Ultrasonic Water, Waste water and Algae Treatment

Ultrasonic technology as an innovative technology used for water and wastewater treatment for pollution removal. This technology acts as an advanced oxidation process. Application of this technology leads to the decomposition of many complex organic compounds to much simpler compounds during physical and chemical compounds during cavitations process.

Introduction

Ultrasound irradiation is a novel advanced oxidation process that has emerged as an answer to the growing need for lower levels of contaminants in wastewater. The basis for the present-day generation of ultrasound was established as far back as 1880 with the discovery of the piezoelectric effect by the Curies. Cavitations phenomenon was first identified and reported in 1895. Destruction of microorganisms by ultrasonic has been of considerable interest since 1920’s when studies of Harvey and Loomis were published. They showed that heating injure the bacteria, but ultrasonic appeared to have a greater effect. Since l945, an increasing understanding of the phenomenon of cavitations has developed coupled with significant developments in electronic circuitry and transducers (i.e. devices which convert electrical to mechanical signals and vice versa). As a result of this there has been a rapid expansion in the application of power ultrasound to chemical processes, a subject that has become known as “Sonochemistry”. In the 1960’s, research concentrated on understanding the mechanisms of ultrasonic interaction with microbial cells. Cavitations phenomenon and associated shear disruption, localized heating and free radical formation were found to be contributory causes. By 1975 it was shown that brief exposure to ultrasonic lead to thinning of cell walls which was attributed to release cytoplasm membrane from the cell wall. Fecal coliforms inactivation most likely results from a combination of physical and chemical mechanisms which occur during acoustic cavitations, so it is expected that higher intensities will enhance inactivation rates. However, for most processes, increase in process rate not continues with higher sound intensities. Since 1990, several studies have focused on the use of ultrasound to remove organic xenobiotics from water.

Sound theory

Most modern ultrasonic devices rely on transducers which are composed of piezoelectric materials. Such materials respond to the application of an electrical potential across opposite faces with a small change in dimensions. This is the inverse of the piezoelectric effect. If the potential is alternated at high frequencies, the crystal converts electrical energy to mechanical vibration (sound) energy. At sufficiently high alternating potential, high frequency sound (ultrasound) will be generated. When more powerful ultrasound at a lower frequency is applied to a system, it is possible to produce chemical changes as a result of acoustically generated cavitation. Frequencies above 18 kHz are usually considered to be ultrasonic. The frequencies used for ultrasonic cleaning, range 20 kHz to over 100 kHz. The most commonly used frequencies for industrial cleaning are those between 20 and 50 kHz. Ultrasound has wavelengths between successive compression waves measuring roughly 10 to 10-3 cm. These are not comparable to molecular dimensions. Because of this mismatch, the chemical effects of ultrasound cannot result from a direct interaction of sound with molecular species. .

Advantages and disadvantages

There are no additives introduced into the ultrasonic system and no by products generated by ultrasonic technology. Therefore, there are no anticipated environmental concerns associated with

this technology . In contrast to many other processes which are negatively affected when suspended solids of effluent increase, efficiency may even improve by increase of turbidity or suspended solids.

Ultrasound applications

In recent years, considerable interest has been shown in the application of ultrasound as an advanced

oxidation process for the treatment of hazardous contaminants in water. Sonochemistry has been demonstrated as a promising method for the destruction of aqueous pollutants.

1- Applications of ultrasound in phenolic effluents treatment

Phenol is one of the most abundant pollutants in industrial wastewater. Phenol is released to

the environment from industries such as petroleum refining, coal tar, steel, tanning, pesticides,

pharmaceuticals and etc.. Phenol has attracted public attention due to its presence in groundwater, rivers and drinking waters. Phenol even in small quantities causes toxicity and foul odor to the water. Most of the countries specify maximum allowable concentration of phenol in effluent to be less than 1 ppm . Several treatment methods such as chemical oxidation, biological treatment, wet oxidation, ozonolysis and activated carbon adsorption have been proposed for the removal of phenol from industrial effluents. In recent years advanced oxidation processes (AOPs) was developed. One of these technologies is hotolysis. This method is based on supplying energy to chemical compounds as radiation which is absorbed by reactant molecules that can pass to excited states and have sufficient time to promote reactions. Direct photolysis has been always considered as one possible alternative because it is possible for molecules of most organic ompounds to transform, to cleave bonds and even to undergo complete destruction in the presence of UV eradiation.

2- Algae removal

A novel method to inhibit growth of algal population is application of ultrasonic irradiation. Ultrasonic irradiation in a liquid medium has been used for many years to lyse biological cells. Ultrasonication may have the potential to reduce their capacity to float and control their buoyancy there by reducing their concentration near the surface of water bodies and reduction their growth and survival. Ultrasonication may also inhibit or reduce growth of algal population through its affect on metabolic processes.

Application of ultrasonic irradiation to control algae population was evaluated in the results showed that exposure to ultrasonic irradiation collapsed algae gas vacuoles, which results in loss of buoyancy and regulating ability and thus localizing the cells. By long term say 3 to 4 weeks of sonication of pond or swimming pool or cooling tower the algal population were destroyed.

3- Nematode Removal

There are more than 15,000 known species of roundworms and several thousands of individual

nematodes. Conventional water treatment processes are not highly effective in nematodes removal.

Nematodes are very resistant to inactivation by free chlorine and can pass through rapid

sand filters. One approach nematode inactivation is ultrasonic. In a research it has been shown that exposure to ultrasonic irradiation results in destruction of nematodes. 12 min sonication destroys 100% of the nematodes. Also results show that increasing of sonication time has a considerable effect on nematode removal.

4- Coliform Removal

Sonication for long time has a significant effect on bacterial kill. When ultrasonic is used to sonicate liquid containing large volumes of bacteria at particular frequency, there is a resultant in the intensity of ultrasonic entering the system. Furthermore, it showed removal efficiency is highest.

It is to say that 99.95% reduction in bacteria concentrations were achieved with the majority of these reductions found to occur in due course of time.

It is possible to decrease the number of organisms present in the water and that the process depends on exposure time, frequency and intensity of the ultrasound irradiation, as well as on the type of organisms.

It shows that the efficacy of various advanced oxidation processes based on ultraviolet, Ozone , Chlorine, H2O2 and ultrasound irradiation to inactivate Escherichia coli in sterile water and total coliforms (TCs) in biologically treated municipal wastewater found that H2O2-assisted UVA/ TiO2 photocatalysis (9 W lamp) could generally lead to nearly complete E. coli destruction in 20 min with the extent of inactivation depending on the photocatalyst type and loading and oxidant concentration.

5- Organic matters

Results of a study show that Ultrasound reduces BOD5 of secondary effluent, Suspended BOD5 was removed completely (approximately 100%), however soluble BOD5 was increased in some cases. Efficiency of total COD removal was determined to be 17-28%. Removal of suspended COD is better accomplished than SCOD. In this study most of COD removal was accomplished in initial sonication time and removal efficiency was not much increased by time. Better organics removal from secondary effluent is performed at 130 kHz compared with the lower frequency. Efficiency of treatment in 60 min

Treatment of raw sewage by sonication +uv or ozone (combined sonication and UV irradiation or ozonation ) significantly reduces COD . Ultrasonic can decompose other organic substrates such as chlorinated hydrocarbons, pesticides, phenol, explosives such as TNT, and esters, and transform them into short-chain organic acids, CO2 and inorganic ions as the final products. The time for complete degradation ranges from minutes to hours. The application of ultrasound to remove low- concentration bisphenol A (BPA) in aqueous solution at the particular frequency, and ultrasonic intensity and ozone will remove BPA removal . BPA was degraded under Ultrasound in the presence of CCl4. Also they identified the main intermediates resulting from BPA ultrasonic degradation by GC-MS. They found that OH radical induced oxidation is the major destruction pathway during BPA sonolysis. The degradation of bisphenol A (BPA) upon ultrasonic action under different experimental conditions and evaluation of saturating gas, BPA concentration, ultrasonic frequency and power has

been studied. They found that for 118 μmol/L BPA solution, the best performance obtained at

5- Fungi removal

The results of disinfection during sonicating 500 ml fungi suspension at eight different samples (200, 1000, 2000, 3500, 5500, 6500, 10000 and 17000 CFU/ml). Number of fungi decreases with increasing in disinfection period. Results showed that increasing in disinfection time

has considerable effect on fungi reduction. Also, there is no significant reduction of fungi in less

than 15 min exposure time to 42 kHz but considerable levels of reduction can be expected after longer periods (99.92%). It is suggested that USRT at a frequency of 26 kHz is capable to some degree of inactivating fungi cells. Experiments at 42 kHz can be seen to be more effective than operation at less than this frequency. In another study it was suggested that in a squeeze- film-type sonicator, more than 90% inactivation of fungi was achieved for 60 min. In this experiment, sonolytic inactivation of fungi cells was investigated using a horn-type sonicator at 27.5 kHz frequency. Results of the fundamental investigation included effect of USRT power, cell numbers, and flow rate on the inactivation of the fungi cells using a horn-type sonicator and a squeeze-film-type sonicator. Inactivation by USRT was fastest at the lowest initial cell numbers.

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