production. In some states, due to ambient temperature, it was not
possible to run the proposed bioenergy facility all over the year.
According to Wigmosta et al. [34] algae production in the open
pond was not possible below 10 C. The number of cycles operated
in each state was estimated based on average temperature of each
month. For example, in Florida, year round algae production could
be possible (8 cycles) whereas in Minnesota only 3 cycles were
possible. Temperature dependent growth of algae was not considered
in this study as the growth and temperature relationship was
species specific. Anaerobic digestion and enzymatic hydrolysis
were introduced to recover nutrients (N, P) from the residual biomass
left after biodiesel production. Recovered nutrients were
used to produce algal biomass for the next cycle (Fig. 1). Unused
nutrients (N, P) in the algal ponds were also recovered through
centrifugation and recycled back to the algal pond for use in the
next cycle. In the first cycle, recovered nutrients from dairy waste
through AD were used for algal biomass production. In the second
cycle, a part of the nutrients from the first cycle, bound to algal
biomass, was recovered through AD, enzymatic hydrolysis, and
used for additional algal biomass production. In the subsequent
cycle more nutrients were recycled which were originated from
the previous cycles.