For each scenario, minimum nonrenewable primary energy
requirement (NRPER) (Case A and B scenarios) achieved was plotted
along with the maximum variation in NRPER. In the scenario 0,
minimum NRPER was the lowest (0.35) followed by the first scenario
(0.37), whereas the minimum NRPER for 2nd, 3rd, and 4th
scenarios were 0.51, 0.55, and 0.70 respectively [Fig. 3].
Therefore, NRPER in each scenario was less than one.
Incorporating reference scenario and nutrient values of applied
sludge, residual biomass, could not change the NRPER for each scenario
for case A. Variation in NRPER was also observed with
increase in number of cycle (scenario 1–4) (Fig. 3). Variation in
NRPER with increase in number of cycle was attributed to the following
reasons (i) increasing recovery of water, nutrients from the
algal ponds and residual biomass, through pumping and anaerobic
digestion, (ii) variation in production of algal biomass, which is
dependent on the N/P ratio in the algal pond, and (iii) bioenergy
produced in the form of excess biogas, which was dependent on
the biogas produced and heat energy required, for the whole
bioenergy production process (Fig. 3), and (iv) variation in number
of cycle executed in different states