Around 1.3 billion tonnes of food are wasted worldwide per year, which is originally produced under extensive use of energy and nutrients. Use of food waste as feedstock in biotechnological processes provides an innovative way to recover parts of the energy and nutrients initially spent on food production. By chemical and biological methods, food waste is hydrolysed to glucose, free amino nitrogen and phosphate, which are utilisable as nutrients by many microorganisms whose metabolic versatility enables the production of a wide range of products. Microalgae are particularly of interest as chemicals, materials and energy are obtainable from microalgal biomass after chemical and/or biological modifications. In this review, valorisation of food waste in biotechnological processes is presented as an additional option to green chemical technologies.

The effects of salinities between 10 and 30 psu on the growth of blue mussels, Mytilus edulis, were studied in laboratory feeding experiments and compared to the growth of mussels suspended in net-bags in the brackish water Great Belt, Denmark. In the laboratory, 3 series of growth experiments were conducted: in Series #1, groups of mussels were exposed to 10, 15, 25 and 30 psu, in Series #2, two groups of mussels were exposed to 10 and 30 psu, respectively, for 15 days (first period) where upon the mussels were exposed to the reversed salinities for another 15 days (second period). In Series #3, two groups of mussels were initially exposed to 15 and 25 psu for 22 days whereupon the mussel groups were exposed to the reversed salinities for another 17 days. In the laboratory experiments there was a tendency towards reduced growth with decreasing salinity, reflected as reduced shell growth rate and decreasing weight specific growth rate with falling salinity. The shell growth rate was relatively low in the first feeding period compared to the second period, and mussels that were initially exposed to 10 psu, where the growth was low, exhibited fast growth when subsequently exposed to 30 psu, and reversed when 30 psu mussels were exposed to 10 psu. The study showed that mussels are able to adjust growth at changing salinities, and the observed effect of salinity could partly be explained by a temporary shell valve closure after a sudden change in salinity. The specific growth rate of mussels measured in laboratory experiments at salinities between 15 to 25 psu (4.2% to 4.8% d -1 ) were comparable to the growth of mussels in the field experiment (3.2% to 4.0% d -1 ) where the salinity varied between 24 and 13 psu during the growth period.

Biotechnological processes are promising alternatives to petrochemical routes for overcoming the challenges of resource depletion in the future in a sustainable way. The strategies of white biotechnology allow the utilization of inexpensive and renewable resources for the production of a broad range of bio-based compounds. Renewable resources, such as agricultural residues or residues from food production, are produced in large amounts have been shown to be promising carbon and/or nitrogen sources. This chapter focuses on the biotechnological production of lactic acid, acrylic acid, succinic acid, muconic acid, and lactobionic acid from renewable residues, these products being used as monomers for bio-based material and/or as food supplements. These five acids have high economic values and the potential to overcome the "valley of death" between laboratory/pilot scale and commercial/industrial scale. This chapter also provides an overview of the production strategies, including microbial strain development, used to convert renewable resources into value-added products.

Experimental feeding and growth studies on filter-feeding organisms often rely on constant algal concentrations maintained over extended periods of time. Here we present a fluorometer controlled apparatus (FCA) designed for feeding experiments with suspension-feeding mussels at naturally low chlorophyllaconcentrations above 0.5 µg L−1. The principle used is feedback regulation of the algal concentration based on continuous monitoring of the fluorescence intensity of chlorophyllain water pumped through the apparatus from an aquarium with mussels. The filtration rate is monitored continuously as the rate of change of measured volume of an algal stock added to the aquarium for keeping a constant algal concentration. As an example, the FCA has been used to study the filtration rates of blue mussels (Mytilus edulis) at algal concentrations both near and above the incipient saturation level for reduced filtration activity. As another example to put the FCA into perspective as a reliable method for environmental effect studies, the apparatus has been used to demonstrate the acute effect of changing salinity on the filtration rate ofM. edulis.

We have investigated changes in specific contents of protein, glycogen and lipid, and fatty acids of blue mussels, Mytilus edulis, under different conditions in the field and in laboratory feeding experiments using different microalgae. Specific contents of glycogen and lipid increased in mussels relocated to net bags at a location in Kerteminde Bay (Great Belt, Denmark) in contrast to mussels relocated to a location in Sallingsund (Limfjorden, Denmark). The polyunsaturated fatty acid, eicosapentaenoic acid, reached 3 times higher values in the mussels in Kerteminde Bay. Mussels fed pure cultures of Crypthecodinium cohnii, which is rich in the polyunsaturated fatty acid, docosahexaenoic acid, and glycogen, gained the highest specific contents of this fatty acid and glycogen. Mussels feeding on the most protein rich of the microalgae, Bracteacoccus sp., gained the highest protein contents. The specific glycogen content of the mussels was influenced by their “condition” (body dry weight/shell length ratio) while specific protein and lipid contents were not. Starvation affected mainly the specific glycogen content. These results show that biomass composition of blue mussels is affected by living site and local phytoplankton species and that the fatty acids composition of mussels reflects the content of fatty acids in the diet.

Mussel larval densities may fluctuate considerably on both small spatial and short temporal scales. So far, only few and scattered data on the occurrence of mussel larvae have been reported from Danish waters. However, seasonal variation in density of blue mussel (Mytilus edulis) larvae as related to environmental factors (temperature, salinity, phytoplankton biomass) is basic information of relevance for future line-mussel farming in Danish waters. Here we report on the density of mussel larvae in a number of potential farming sites in the inner Danish waters. The mussel larval density measured in Skive Fjord, an eutrophicated inner branch of Limfjorden, during a period of 20 years, from 1989 to 2009, along with corresponding temperatures and chlorophyll a, makes up the most important series of data reported here. In most years, a pronounced spring density peak and a subsequently lower autumn peak could be seen in Skive Fjord, but most conspicuous in the period 1993 to 2002 where the mean maximum spring larval density was 319 ± 260 ind•l −1. Further, data on mussel larval densities have been recorded on 4 locations in the Great Belt region: Kerteminde Bay in 2008 to 2011, and in 2008 at 3 other locations: Musholm Bay, Svendborg Sund, and Horsens Fjord. The maximum spring densities in the studied waters were observed in Skive Fjord, typically in May, whereas 10 to 100 times lower peak densities were found at the other locations studied. The reported observations show that mussel larvae are omnipresent in the studied areas and it is suggested that the larval density is sufficient for recruitment to future linemussel farms.

Mussels from two sites within the Baltic mussel (Mytilus edulis × M. trossulus) hybrid zone were used in a comparative study on the effects of salinity-changing rates on filtration activity. The acute effect of varying salinity-changing rates was found to be similar in M. edulis from the brackish Great Belt and in M. trossulus from the low saline Central Baltic Sea, and the relationships could be described by linear regression lines through 0.0 indicating that the acute effect of deteriorating conditions at decreasing salinities is the opposite as for improving conditions when the salinity is subsequently increased. Further, both M. edulis and M. trossulus acclimatized to 20 psu reacted to an acute salinity change to 6.5 psu by immediately closing their valves whereupon the filtration rate gradually increased during the following days, but only M. trossulus had completely acclimatized to 6.5 psu within 5 days which may be explained by different genotypes of M. edulis and M. trossulus which probably reflected an evolutionary adaptation of the latter to survive in the stable low-salinity Baltic Sea.