Issues and Challenges Associated with Cleaning Waste Water Using Algae
Cleaning up the wastewater generated by STP’s and industrial waste water treatment plants are not as easy as it sounds.
There are several challenges associated with growing algae in such conditions. The algae-based wastewater treatment technology is highly dependent on several environmental conditions most of which have been discussed in this blog post.
Some of the key challenges that are associated with algae-based waste water treatment include:
1. Land Requirement: The principal disadvantage of algae pond systems are that they require much larger areas of land than other forms of sewage treatment.\
2. Light Requirements Light requirements vary greatly with the culture depth and the density of the algal culture: at higher depths and cell concentrations, there is a requirement for high light intensity to penetrate through the culture. For this reason, almost all open algal culture systems are shallow, with depths ranging from about 15 – 30 cm. This fact shows that increasing cell densities (increasing chlorophyll) rapidly reduce the amount of light reaching the algae deeper in pond, leading to light limitation of the cells.
3. Temperature: Temperature directly influences the physical, chemical and biological activities in a waste stabilization pond system. Rate of photosynthesis and cellular metabolism are directly proportional to the pond temperature. Ponds should be designed for most adverse temperature conditions. At lower temperature, dissolved oxygen present has a tendency to remain in pond longer. As the temperature rises, dissolved oxygen is likely to be liberated to atmosphere, especially under supersaturated conditions.
4. Rainfall: Rainfall influences pond performance. Detention time reduces when it rains. Besides, heavy shower dilutes the contents of shallow ponds reducing the food available to biomass. Rainfall adds oxygen to a pond system by increasing turbulence. Often heavy rainfall causes overflow in ponds resulting in contamination of soil, ground water and nearby water bodies with untreated or partially treated sewage water.
5. Mixing: Mixing affects algae in several ways. Vigorous mixing increased the flashing light effect, removed excess dissolved oxygen, effectively improved the CO2 supply, and resulted in higher productivity (Laws et al., 1983; Richmond & Vonshak, 1978). However, from the economic point of view, a high aeration rate will lead to higher running costs since mixing requires energy, so that it is not recommended for the large-scale production of microalgae.
6. Harvesting: Harvesting Algae, especially microalgae, cannot be easily harvested and the algae-laden water is often released into effluent receiving stream. Technical and economic problems in algal harvest are largely due to the size, specific gravity, and morphology of the algal cells, their limited concentration and low market value. Species like Oscillatoria, Micractinium, Spirulina and Scenedesmus are desirable for harvesting purposes because of their larger size and more complex shape as compared with the single cellular forms such as Chlorella and Oocystis, which are difficult to concentrate.
7. Contamination : Growing specific strains of algae in wastewater is very difficult. Algae-based wastewater systems can get easily contaminated and take-over by other undesirable algae strains. Most algal culture failures are due to contamination. More details about the challenges faced due to contamination will be discussed in detail in the upcoming blog post.
8. Other Challenges:
Some problems associated with pond systems used for algae-based wastewater treatment are:
(a) Scum Control: Scum is a common characteristic usually present in the spring when the water warms and the biological activity resumes. Scum can promote a blue-green algae growth which can give rise to disagreeable odors. If scum is allowed to accumulate, it can cut off the sunlight from the pond which would affect the dissolved o\xygen produced from photosynthesis.
(b) Odor Control: Odors are usually associated with overloading and poor housekeeping. Most odors usually occur during the spring warm-up when biological activity resumes. Reduction of odors can be accomplished by the use of surface aerators and the addition of chlorine. In some cases, sodium nitrate has been used as a supplemental source of oxygen.
(c) Weed Control: Weeds are mostly objectionable because they can promote mosquito breeding and scum accumulation. Aquatic weed roots may puncture pond linings and hinder pond circulation.
(d) Mosquito Control: Another major drawback with waste stabilization ponds are breeding of mosquitoes, which often resulted in the outbreak of malaria more frequently. \Communities around the ponds (< 300 m) suffer malaria more frequently than those who live far away (> or = 300 m).
(e) Insect Control: There are also many minute, shrimp-like predators which feed on algae, usually during the warmer months, and may clear the pond of algae, reducing the dissolved oxygen content in the pond and producing noxious odors. This condition is normally temporary. Effective insect control is usually accomplished by good housekeeping practices and the use of insecticides.
(f) Oxygen Depletion – In certain instances, algae blooms die due to environmental conditions such as low temperatures, high toxic environment, increase in pH, low concentration for nutrients, etc. These dead algae sink to the bottom of the pond and get degraded. The degradation of algal constituents requires oxygen which contributes to increase in BOD and nutrients such as phosphorus and nitrogen.
(g) Cost-effective harvesting procedures such as natural settling could result in long harvesting durations.
(h) Evaporation losses may occur in hot, dry climates, which significantly reduce the amounts of treated wastewater available for agricultural reuse.
Read more from Oilgae’s Algae-Based Waste Water Treatment – The one and only such report in the world Oilgae has published a unique report to assist those keen on understanding the algae-based waste water treatment technology and those wanting to venture into this industry. The Oilgae’s guide to waste water treatment is a comprehensive guide to understanding the algae-based waste water treatment, technolgies, challenges and the players that are involved in this industry. Link –http://www.oilgae.com/ref/report/wastewater_treatment/wastewater_treatment.html
Read Related Blogs:
Solving the Issues of Current Waste Water Treatment Practices Using Algae
Commonly Used Algae Strains for Waste Water Treatment
Microalgae and Waste Water Treatment – Why Employ Algae to Clean Up Waste Water?
Algae Clean Waste Water to Produce Numerous Useful Products
