Single cell protein could lead to an undesirable change in them. This is particularly important in continuous culture, which is often used for SCP production. Here the long growth period (in principle indefinite but in practice several weeks)can be long enough for mutants to arise, compete with the parent organism and predominate In batch culture there is not enough time for this to occur vii) Advantage. For most SCP fermentation processes the running costs(costs of operating the fermentation unit) is 10-20% of the total production cost. Aeration costs contribute 30-60% to running costs. In other words aeration costs can be much as 12% of the production costs of the sCP. the lower the aeration costs the etter. Production costs for various SCP processes are discussed in more detai later on You are now familiar with the major characteristics of organisms that are useful for SCP production, and the types of substrates on which they can be grown. We are now going to consider in detail the processes that have been developed some of these processes have been developed only as far as the pilot scale, and have not reached commercial operation. Others have reached full production scale but have subsequently failed, for a variety of reasons. These have been included as well as the successes, as they show you the variety in the technology of SCP production, and also show how economic and political factors influence the success and failure of processes. These processes might also become useful and economic some time in the future Emphasis will be put on the technology involved in the fermentation and down-stream processing of each process 4. 6 SCP from carbon dioxide 4.6.1 Spirulina open lagoon Blue-green bacteria(cyanobacteria)of the genus Spirulina have been produced as SCP system in Mexico, using natural bicarbonate-rich ground-water(into which atmospheric COz readily dissolves). A flow diagram of the process is given in Figure 4. 2. The single 10 hectare(1 ha=10,000 m )open lagoon is about 0.6 m in depth and unmixed. The system is operated as a batch culture or as a semi-continuous culture (in which a proportion of the medium is removed and replaced by fresh medium intermittently ). Nitrate is added as a nitrogen source, and other minerals are present in the water. The long filaments are raked mechanically from the pond onto screens(sieves), where water is drained and either recycled or disposed of. The biomass is then de-watered by rotary vacuum filtration, dried by vacuum drying, then dried in a drum drier and ground to a powder (to make the product more appealing). The product contains 56% protein and is sold as The plant operates with an output of 10 g dry weight per square metre per What is the output of the 10 hectare lagoon per year?(Note I hectare=10,000 10 g m2'equates to 10 x 10=10'g ha The daily output is thus: 10 kg ha. day The 10ha lagoon produces 10 kg ha. day This equates to 10 x 365=3.6 x 10 kg year The output of the lagoon is thus 360 tonnes yeaSingle cell protein 69 could lead to an undesirable change in them. This is particularly important in continuous culture, which is often used for SCP production. Here the long growth period (in principle indefinite but in practice several weeks) can be long enough for mutants to arise, compete with the parent organism and predominate. In batch culture there is not enough time for this to occur. Advantage. For most SCP fermentation processes the running costs (costs of operating the fermentation unit) is W20% of the total production cost. Aeration costs contribute 3040% to running costs. In other words aeration costs can be as much as 12% of the production costs of the SCP. The lower the aeration costs the better. Production costs for various s8 processes are discussed in more detail later on. vii) You are now familiar with the mapr characteristics of organisms that are useful for SCP production, and the types of substrates on which they can be grown. We are now going to consider in detail the processes that have been developed. Some of these processes have been developed only as far as the pilot scale, and have not reached commercial operation. Others have reached full production scale but have subsequently failed, for a variety of reasons. These have been included as well as the successes, as they show you the variety in the technology of SCP production, and also show how economic and political factors influence the success and failure of processes. These processes might also become useful and economic some time in the future. Emphasis will be put on the technology involved in the fermentation and down-stream processing of each process. 4.6 SCP from carbon dioxide 4.6.1 Spirulina Blue-green bacteria (cyanobacteria) of the genus SpiruZina have been produced as SCF’ in Mexico, using natural bicarbonaterich ground-water (into which atmospheric CG readily dissolves). A flow diagram of the process is given in Figure 4.2. The single 10 hectare (1 ha = l0,OOO m’ )open lagoon is about 0.6 m in depth and unmixed. The system is operated as a batch culture or as a semi-continuous culture (in which a proportion of the medium is removed and replaced by fresh medium intermittently). Nitrate is added as a nitrogen source, and other minerals are present in the water. The long filaments are raked mechanically from the pond onto screens (sieves), where water is drained and either recycled or disposed of. The biomass is then dewatered by rotary vacuum filtration, dried by vacuum drying, then dried in a drum drier and ground to a powder (to make the product more appealing). The product contains 56% protein and is sold as food. The plant operates with an output of 10 g dry weight per square metre per day. n What is the output of the 10 hectare lagoon per year? (Note 1 hectare = l0,OOO m 1. 10 g m-2 equates to 10 x lo4 = leg ha? The daily output is thus: 10’ kg ha:’ day-’. The lOha lagoon produces Id kg ha:’ day-’. This equates to Id x 365 = 3.6 x Id kg year-’. The output of the lagoon is thus 360 tonnes year -’. open lagoon system