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Nualgi facilitates the growth of diatoms. It prevents the growth of waterweeds, water hyacinth, Green algae and blue-green algae and other waste plants in lakes, ponds, rivers and other water bodies. Other algae like blue Green algae disrupt the ecosystem in water.
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Sludge is a mixture of solid wastes and water, and hence it is usually treated by the method of filtration or sedimentation. Biological methods of sludge removal include processes like coagulation, agglomeration with the help of microbes, etc.
This section provides details on the latest developments and efforts in the Sludge removal process.
We have discussed the following:
- Current Wastewater Treatment Process
- New Technologies for Sludge Removal from Wastewater
- Automated Chemostat Treatment™ (ACT)
- KemiCond Process
- Prospects and Problems of Sludge Pre-Treatment Processes
- Extraction of Extracellular Polymers from Activated Sludge Using a Cation Exchange Resin
Current Wastewater Treatment Process - Sludge Removal
The sludge accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective manner. The purpose of digestion is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids. The most common treatment options include anaerobic digestion, aerobic digestion, and composting. Incineration is also used albeit to a much lesser degree.
Choice of a wastewater solid treatment method depends on the amount of solids generated and other site-specific conditions. However, in general, composting is most often applied to smaller-scale applications followed by aerobic digestion and then lastly anaerobic digestion for the larger-scale municipal applications.
New Technologies for Sludge Removal from Wastewater
Automated Chemostat Treatment™ (ACT) 1
Automated Chemostat Treatment is a novel method in the treatment of sludge. Given below is a brief description of this treatment.
Automated Chemostat Treatment™ (ACT) Overcomes Sludge Disposal and Handling Problems
BPC has pioneered a new, powerful, ecological solution for a range of waste water treatment challenges: ACT – Automated Chemostat Treatment™. The process is flexible and easy to integrate, fully automated, controllable and significantly more efficient than current practices. The results are a virtually sludge-free output of water which can be returned directly into the environment or processed further.
The Innovative Concept: Automated Chemostat Treatment™ (ACT)
The scientific concepts behind ACT are the application of an appropriate bacterial cocktail for a given type of polluted water, and an innovative chemostate. The process is maintained in a balanced state of bacterial growth and organic compound degradation. Because of the low concentration of bacterial cells, no aggregates are formed, and each bacterium acts as a single cell which increases the surface available for the process and enables biodegradation at a much higher efficiency. The BPC-ACT™ operates as a continuous flow reactor without using activated sludge. The bioreactor can thus be applied on site while using available infrastructure with high flexibility for modulation of the process saving dramatically in operational and maintenance costs.
- ACT simplifies the process by reducing bio sludge and chemical usage as well as reducing black sludge creation.
- ACT's flexibility and modularity enables to handle low and high capacities and contamination, to be used for fresh and salt water as well as to be easy modify and Increase capacities.
- Output is virtually sludge-free, meeting strictest disposal standards.
- This trailblazing “green” process is easy to modify and can be used in various sites, including oil refineries, oil storage farms, drilling sites, marine ports, contaminated reservoirs and storage tanks.
Full Control from Any Point for Every Point
The fully automated system is comprised of a variety of on line sensors which feed the control unit information on various parameters such as: TPH, nitrogen, dissolved oxygen, TOC and temperature. The controller ensures to maintain optimum process balance between the flow rate, bacterial growth, additives and organic compound degradation.
The KemiCond® process can be divided into three steps: acidification, oxidation and flocculation. The basic idea is to improve dewatering by breaking down the water - retaining structures which are formed in sludge. Acidification is achieved just before dewatering by treating the sewage sludge with sulphuric acid at a pH below 5. This causes inorganic salts, such as iron phosphates and calcium carbonates to dissolve. The dissolution of salts contributes to a sludge volume reduction. Oxidation is achieved by adding hydrogen peroxide, H2O2 – a strong oxidizing agent. In the presence of various transition metals hydrogen peroxide decomposes into hydroxyl radicals. The very high oxidizing potential of this radical is readily used in the KemiCond® solution. Dissolved iron (II) is oxidized into iron (III) which then re-precipitates dissolved phosphorus. This facilitates dewatering and prevents phosphorus from reaching the recipients. The dissolved calcium is removed from the sludge with the filtrate and thus the ash content in the sludge is decreased. Extracellular polymeric substances (EPS), the sticky organic matter produced by microorganisms, are also oxidized which changes the sludge structure. This new structure makes the sludge easy to handle both at the plant and during the disposal transport. Furthermore, addition of hydrogen peroxide does an excellent job in reducing odours, as it oxidizes organic matter such as mercaptans and sulphides. And last – but certainly not least – the hydroxyl radicals will lead to a hygienisation of the sludge. Flocculation is the third and last chemical treatment phase in the KemiCond® solution. 2
Pre-treatment processes have been developed in order to improve subsequent sludge treatment and disposal. Disintegration of sludge solids in the aqueous phase changes the sludge structure and solubilizes organic matter. This paper provides an overview of the applications of wet disintegration in wastewater and sludge treatment. Applied disintegration techniques such as mechanical, thermal, chemical and biological methods are briefly described. The methods are compared regarding energy consumption, operational reliability and stage of development for application on wastewater treatment plants. Mechanical and thermal methods appear to be most suitable at this stage. The effects of pre-treatment on subsequent sludge treatment processes and the wastewater treatment are described. The performance of various methods is assessed. For the improvement of stabilization, mechanical and ozone treatment as well as thermal treatment performs best. Dewatering can be enhanced by thermal and freeze/thaw treatment. All methods show positive effects in the reduction of the number of pathogens. Pre-treatment leads to secondary effects like the generation of recalcitrant compounds and odor, which is mainly a problem of thermal and ozone treatment. The evaluation of capital and operational costs is difficult, because of the lack of full-scale experience. Especially thermal, freeze/thaw and biological treatments can be realized at low costs if the conditions are appropriate. Nevertheless, the economic efficiency has to be investigated critically for each individual application.3
Extraction of Extracellular Polymers from Activated Sludge Using a Cation Exchange Resin
The extraction of water soluble extracellular polymeric substances (EPS) from activated sludge was investigated. The extraction procedure was based upon cation exchange using a cation exchange resin (CER). Activated sludge from two different types of treatment plants responded very similarly to the extraction procedure. The EPS yield was enhanced by increasing the stirring intensity, the amounts of CER added and by increasing the extraction time. For the chosen extraction procedure the yield was twice as high as other commonly used procedures. The extract consisted mainly of protein but also humic compounds, carbohydrates, uronic acids and DNA were found in significant amounts. The extracted amounts and relative fraction of the individual compounds strongly depended on how the extraction was performed. The ratio between protein and carbohydrate was found in the range 3.9–5.1 depending on the extraction time. Humic compounds and DNA were the compounds most easily extracted. HPSEC investigation of the extract revealed that the extraction did not significantly degrade the EPS. Some cell lysis was identified during the extraction for extraction times greater than 1–2 h by observing a decrease in cell number (stained by DAPI, CTC and acridine orange). The lysis was not considered a significant problem for contaminating the EPS. Measurements of the cell number and cell size distribution in the sludge suggested that the cell mass did not account for more than approximately 10–15% of the total organic fraction of the investigated sludge. Two extraction strategies were formulated. Analytical methods for analysis of sludge and EPS extracts were compared and discussed. A corrected Lowry method for analyzing protein as well as humic compounds was implemented and found suitable.4
3 Muller JA, 2001, Prospects and problems of sludge pre-treatment processes. Water Sci Technology, 44(10):121-8.
4Bo Frølund, Rikke Palmgren, Kristian Keiding and Per Halkjær Nielsen, 1996. Extraction of extracellular polymers from activated sludge using a cation exchange resin, Water Research, 30 (1749- 58).