Their construction is usually two concentric rotating blades surrounded by a stationary casing. Solids enter the decanter settle on the bowl wall to be discharge, while the clarified liquid is discharged at the other end .The centrifugation process has presented itself as a very reliable and effective method of microalgae harvesting but the capital cost can be high and the energy consumption level is considerable. Although centrifugation is a proven technology for the fast and effective means of harvesting most microalgae, its use and the high capital and operational cost, must be considered in conjunction with the scale and value of the product. Decanter type centrifugation has the benefit of removing a lot of the water during the algae harvesting process reducing the dewater requirements. The dewatered biomass using the decanter centrifuge is much more concentrated than that achieved using the disc centrifuge . Wastewater from local industries or agriculture often contain contaminates that increase the yield of microalgae, nft channel whilst at the same time reducing the operational cost of cultivation. Thus, some wastewaters can be used as both carbon and nitrogen sources for cultivation of microalgae .

The added advantage of using wastewater is the opportunity of the microalgae plant doubling as a water treatment plant returning water that may be suitable for re-use to its source. Cultivation of microalgae in wastewater for biodiesel production is highly desirable since it leads to a significant reduction in the production cost and reduction in the demand for freshwater with the con-cominitant removal of varies contaminants, such as phosphorus, nitrogen, heavy metals, and pathogens from the waste water.Further research of wastewater availability and treatment in the Port Headland region would be required to determine if a significant improvement in the efficiency and viability of the plant can be achieved. This research is beyond the scope of this paper and would need to be explored in future papers.  A major event in the human story is the transition of man from hunting and gathering to subsisting on cultivated plants and domesticated animals. Evidence indicates that this transition originated in the Near East some ten thousand years ago, mainly in a region known as the Fertile Crescent.

These reasons include environmental factors such as climatic changes, environmental stress and the lack of means of subsistence , as well as factors that relate to human behavior such as changes in the complexity of human society, the development of permanent settlements, concentration of populations in certain areas and even spiritual and ceremonial factors. Several authors indicated an additional factor, namely the tight link that exists between the bio- logical evolution of farming societies and the evolution of cultivated plants. This link, brilliantly championed by Rindos  in fact underlies the phenomenal success of both humans and their crops. One may wonder how it happened that manturned recently into a species with such a dazzling ability to subsist and re- produce; and at the same time, how it happened that plant species such as wheat or maize, whose incidence in the wild is relatively limited, “took over” vast expanses of land worldwide. It appears that in order to understand the initial transition of the hunter-gatherer societies to farming, and then,hydroponic nft the rapid spreading and domination of farmers and agriculture throughout the world, one must examine the relationship between the following two elements: changes in the genetics and dispersal patterns of cultivated plants, and concurrent changes in human behavior. It will be discussed below how these two changes led directly to a higher biological fitness, to an increase in human populations and in the spreading of their crop fields, and in turn, to the rapid domination of the entire world by farmers and their crops. That is, the virtually symbiotic co-evolution of plants and man.

Two notes are necessary at this instant: firstly, the defining of bio- logical fitness is beyond the scope of this paper and it will be regarded hereby simply as the ability to generate fertile offspring. Secondly, this paper focuses solely on the Near East as a case study for the origin and spread of agriculture but it may be found relevant to other worldwide regions as well. The dependence of human societies on cultivated crops  is absolute. The large crops obtained by agricultural processes are what enabled the significant growth in human population, its existence and success. On the other hand, the existence and thriving of the cultivated crops too depend entirely on the growers, that is, on man. It is obviously clear, that today, an irrevocable dependency has been formed be- tween man and his crops.