Treatment of Domestic and Industrial Wastewater Using Algae Strains Critical Analysis and Review

Treatment of Domestic and Industrial Wastewater Using Algae Strains: Critical Analysis and Review

Wastewater comprises of liquid or water carried wastes coming from sanitary conveniences of residences, commercial or industrial buildings and facilities; in addition, to other ground water, surface water, and storm water if present. Untreated water has high levels of organic material, pathogenic organisms, nutrients and many toxic elements. Therefore, this type of wastewater poses as an environmental and health danger; hence, calling for moving such waste from its sources and treat it appropriately before disposal [1]. The primary objective of wastewater management is to protect the environment in a way to align with public health and socio-economic concerns. For this reason, wastewater management is becoming vital because of diminishing water resources, increase wastewater disposal costs and strict discharge regulations that have lowered possible contaminant levels in water bodies.

The significance of water as a worldwide resource for human life is irrefutable. For this indisputable reason, people in the globe feel it is a requirement to protect this important resource such that it has become a conservation priority globally. Therefore, this has seen to the advancement in the efficiency, convenience, and sanitation of the human society owing to the establishment and distribution of large-scale dependable supplies of high quality water. In so doing; however, the same establishments allow the convenient disposal of infectious and hazardous effluents form their sources, and generally, into any water body [2]. This aqueous, or wastewater and the activities included, such as the correction of the situation, which form the basis of this thesis.

Although there are many treatment practices, some of them generate a lot of sludge that needs off-site disposal. In addition, many of the wastewater treatment activities cannot efficiently variations in the composition of wastewater. This means that a treatment process, which may have efficiency in treating wastewater in some time of the year, is not proficient in treating wastewater in other times of the year. This paper is an analysis of researches on algae for wastewater treatment. On the contrary, a system based on algae, proved to have interesting advantages over conventional methods of wastewater treatment. Algae-based water treatment is cost effective, requires low energy, reduces the formation of sludge, and generates useful algal biomass [3].

Summary

The notion of algae-bacteria culture as an engineered system in domestic and industrial wastewater treatment has witnessed increased force over the past decades. This system works well in regions that experience high solar radiation and temperature because the removal is a natural process. When solar radiations fall on the algae, they react by producing oxygen, which aerobic bacteria may use to biodegrade pollutants, whilst the algae take in the carbon dioxide released from bacterial respiration [4]. In so doing, the algae provide an affordable and safe alternative to mechanical aeration; additionally, it ends up contributing to carbon dioxide mitigation. This technology is efficient because nitrogen and phosphorous could accumulate into the algae bacterial biomass during the removal process.

The disadvantage of adopting this technology is the requirement for cost-effective biomass harvesting methods. For this reason, there is a need to apply a technical separation unit comprising of centrifugation, which will in turn raise the cost. Utilizing chemicals such as Calcium, or Slaked lime in the technology, will result in secondary pollutants [5]. Incorporating an immobilization with the technology is a possible solution; however, all media are expensive and ineffective over a long period of operation. Therefore, there is a need to adopt an efficient biomass harvesting strategy such as a settle able algae-bacteria system. Although previous studies touched on identification and biometry of the dominant algal species, the studies lacked sufficient information about the bacterial community associated with the process [4].

Review

According to [6] Algae play an important role in the natural self-purification of contaminated waters. This phenomenon, for natural algal treatment, moreover, cannot happen without biological intervention. Early studies comment that this kind of association qualifies as an interrelationship or mutual "symbiosis" between algae and bacteria. In addition, Bartsch in his, research comments that, bacteria and algae are the most dominant organisms among the plank tonic biota of oceans with their association metabolism help them in controlling pelagic energy flow and nutrient cycling in aquatic environments. The treatment of concentrated wastes depends on these microbiological processes to accomplish the treatment.

In addition, [6] further comments that a WSP serves as a reactor that intensifies waste concentrations, resulting in an accelerated rate of "naturally occurring" waste treatment and the purification processes. At the center of this natural biological process is the cyclic synergistic relationship amid algae and bacteria. However, the author, in his research suggests that certain fungi play a substantial role in this algal-microbial stabilization of organic effluents within WSPs such that the metabolic elements of fungi bacteria and algae have a correlation. Apart from [6] there are other studies on the role of algae in wastewater treatment, providing a discussion and research within literature with the biochemistry now strongly developed.

The above figure is an example of a developed model of a concise process overview, with algal-bacteria interrelationship central in the [6]. It is a process showing the "Cyclic symbiosis" amid algae and bacteria within a WSP environment.

Elaboration of the above process

Heterotrophic microbial mineralization of incoming organic materials generates carbon dioxide (CO2), ammonia-nitrogen (NH3 -N), phosphates (PO 43- ) and essential vitamins. All these by-products are stable, inorganic and oxidized. Afterwards, the autotrophic algae utilize the synthesized products of bacterial metabolism for their own development and growth through photosynthesis. In addition, the splitting of the water molecules, during the course of algal photosynthesis, provides oxygen for aerobic microbes to allow for oxidative decomposition of wastewater organics; therefore, the process continues in this "positive feedback" cycle. The aquatic chemistry showed in the figure accounts for the diurnal shifts in dissolved oxygen (photosynthesis and respiration), PH (carbonate-bicarbonate) mostly seen in WSPs.

Using Aquatic Plants

Several studies did refer to the capacity of aquatic plants to get nutrients from the water in which they survived. The main reason, which has prompted the rise in the papers within the last decade on the nutrient extraction possibilities of water plants is the increase in awareness of the problems of water pollution both fresh and salt water resulting from population increase, industrial development, human disposal, animal and industrial wastes into water bodies [1]. Many of the examples of devastating effects of the wastewater on previously clean rivers and lakes aroused public and scientific consciousness on the need to arrest the practice of disposing but try to reverse the process by extracting the pollutants [1]. The exceptional ability of water plants have the ability to extort compounds and elements from water effectively is well organized.

According to [7], he suggested a method for reducing water pollution by harvesting water plants, which have extracted nutrients from the water. The author comments that all water plants can serve this purpose; however, small plants or submerged plants are difficult and expensive to harvest compared to floating and emergent vascular plants. For instance, [7] suggests that the water hyacinth covers 10% of the pond and can serve well in removing adequate nutrients to avoid excessive phytoplankton development. In addition, the author suggests that the water hyacinth has the ability to extract nitrogen and phosphorous under good developing conditions.

Practical Application of Algal Treatment Process

According to a recent report by Oligae, using algae-based wastewater treatment is cost effective, requires low energy, reduces sludge formation, reduces emission of GHG and generates significant algal biomass as compared to traditional wastewater treatment method [4]. In addition, in their report, Oligae suggest that algae can make bio-ethanol, bio-butanes, hydrogen and vegetable oil as compared to other crops grown to treat wastewater treatment. In the case of hydrogen production, this resulted when Hans Gaffron, a German scholar observed that algae, Chlamydomonas reinhardtii (a green algae), would at times produce oxygen and switch to produce hydrogen. In addition, algae are significant in generation of biomass, which may play a role in heat and electricity generation [4]. The technology behind algae-wastewater treatment is applicable in various industries including poultry, dairy, aquaculture, textiles, pulp, distillery, leather, foods, petrochemicals, pharmaceuticals, chemicals, mining and metalworking.

Industry

Poultry

Product

Poultry muscle

Effluent description

Fats, proteins, carbohydrates, nitrogen, phosphorous, chlorine, pathogens

Effluent treatment goals

To reduce sludge, remove N, P and neutralize smell and also remove pathogens

Current effluent treatment process

Separation and sedimentation of solids that can float, anaerobic and aerobic treatment, removing nutrients biologically, chlorination and utilizing filters

Algal treatment process

It involves assimilation of nutrients using high rate algal ponds (HRAP)

Process of Algal Treatment Process in Poultry Industry

Source: Oligae report [4]

Evidence-based Research

Materials and Methods

Settle-able algal bacteria culture enrichment

For this evidence-based research, algae inoculum was from the second wall of the Suderburg municipal wastewater treatment plant. This algae solution, was then to settle for one hour, afterwards 30g (wet weight) of it used as algae inoculums for the algal culture enrichment. In the same study, the wastewater obtained from the second clarifier wall, at the same site served as the medium. 600ml of wastewater collected (after preliminary screening, free of grit and primary sediments) served as a bacteria inoculums and a supplier for nutrients. Then, cultivation of the settle-able algal-bacteria took place under laboratory conditions of around 190 C. The photo-bioreactor (for culture enrichment) comprised of a transparent PVC 40cm deep and 29 cm in diameter [3].

Therefore, in estimation, the volume of the medium in the reactor was 14 liters. In addition, the constant mixing, using a magnetic stirring bar, done was to avoid sedimentation of the algae. The tank got radiations from two fluorescent lamps for 12 hours each day. For cultivation of the settle-able algal-bacteria culture to occur, the regular mixing stopped for every 23 hours for an hour and discarded the floating biomass, with a screen. Afterwards, 600ml of the wastewater was replaced after three days in order to uphold a continuous supply of nutrients [3]. After one month of cultivation, there was formation of pea green micro-algae, which had an even distribution in the reactor.

Experimental operation

The same reactor utilized for this research, assisted during the batch mode. However, in this case, the pretreated wastewater served as the feed for the reactor unless stated otherwise. Before beginning the batch experiment, algal-bacterial settled differently: by halting the stirring for 30 minutes. In addition, after every eight days, there was a replacement of 12.5litres of the suspension, with fresh water. The fluorescent lamps provided radiations similarly as in the first experiment, and the photoperiod was 12 hours of light and a 12-hour dark phase. In addition, there was a collection, midway, of 150 samples for further evaluation 4 hours after starting the lighting period.

Results and Discussion

Investigation of the settle-ability of the algal-bacteria culture showed good settle ability because all the biomass settled to the bottom of the glass cylinder within a timeline of twenty minutes, resulting in a decrease of TSS from 1.84-0.016 g/l. The resulting sludge ratio was 12%, showing good settle-ability. The god settle-ability was because of the special cultivation approach in this research. In addition, the interchange in mixing and non-mixing activity in the cultivation period enhanced the choosing of settle-able algae and bacteria providing an efficient way of harvesting algal-bacterial biomass [8]. The harvesting using this technique has three advantages; firstly, there was a reduction in the operating cost because the process did not need extra energy or equipment.

Secondly, there was no addition of chemicals hence elimination of secondary pollutants. Lastly, the settle-ability was applicable for a long-term activity. Sedimentation characterized the cultivated algal-bacterial culture, which did not depend on any immobilization medium. The appearance of the algal-bacteria flocs in the reactor shows that the presence of blue-green algae. In addition, the attachment of wastewater filaments to the algae forms a cooperative system. The cooperation provides support for bio-flocculation leading to the development of settle-able biomass [9]. Several factors such as algae cell surface properties, extracellular polymeric substances, and cations influenced formation and stability of the settle-able algal-bacterial biomass.

Temperature, dissolved oxygen and pH

The variation in temperature, pH and dissolved oxygen had some influence on the treatment process. For instance, the culture temperature, at the start of the process was 12 degrees Celsius. This was probably because of addition of wastewater into the bioreactor after collecting the wastewater. There increase of temperature to room temperature, but remained constant until the end of each batch test. In addition, at the start of the test, dissolved oxygen (DO) was the same compared to the pre-treated water. However, when running the batch test, dissolved oxygen (DO) values reduced to around zero.

This indicated that there was consumption of oxygen generated from the algal photosynthesis, by nitrification, and heterotrophic carbon dioxide oxidation. However, after three days, there was a gradual increase in the levels of oxygen at the end of each test. Additionally, there was no substantial variation in culture pH during the batch tests detected [9]. However, there was a slight pH reduction because of intensive nitrification after the five days. Afterwards, there was a gradual increase in pH. Factors such as micro-algal growth, nitrification, and excretion of basic metabolites due to biodegrading of organic matter have significance influence on pH [3].