respectively. These data indicate t

respectively. These data indicate that (1) all cultures with algae
inoculum showed higher bacterial counts than the control, suggesting
that algae facilitated bacterial growth; and (2) the higher
the initial inoculation, the lower the number of bacteria at maximum,
suggesting that algae also competed with bacteria for certain
nutrients or produced certain substance that limited bacteria
growth. These conflicting observations point to a complex relationship
between algae and bacteria. The fact that the maximum bacterial
numbers for 0.02 g/L algal inoculums concentration was
about 1.5 times higher than for the control suggests that low initial
algal concentration may be more favorable for bacterial growth,
and too low of initial algal concentration may cause bacteria to
bloom and algae to crash.
The bacterial number at high initial algal inoculation was similar
to that of the control and the algal biomass was determined as
the total biomass minus the biomass in control experiments, so the
algal biomass in this study truly reflected the real algal growth.
From the above results, it is obvious that centrate-borne bacteria
have strong influences on algal growth pattern and the biomass
accumulation. The growth of bacteria matched with algal biomass
changes in RC, except for algal inoculums concentration of 0.02 g/L.
Both of them reached the highest yields on Day 2, which indicated
that algae can facilitate the bacteria growth with all inoculums
concentration level within first 2 days, suggesting a mutually beneficial
relationship between algae and centrate-borne bacteria for
the algae inoculums concentration levels used. The statistical significance
of the effect of bacteria to the maximum algal biomass
was evaluated by using ANOVA technique. The p-values of the four
inoculum levels were 0.012, 0.016, 0, and 0.006 with initial algal
inoculums of 0.02 g/L, 0.05 g/L, 0.1 g/L, and 0.2 g/L, respectively.
The p-values were all far less than 0.05, indicating that the effects
of bacteria on maximum algal biomass were significant at high
confidence levels.
This result is partially different from other reports which
claimed that high algal cell concentration would inhibit the bacterial
growth completely probably due to different microbial community
(Xavier Mayali, 2002), while synergistic relationship was
observed in this study (Fig. 2). There are several reasons that
wastewater-borne bacteria and algae may have a symbiotic relationship.
First, bacteria could supply sufficient carbon dioxide
which is required for algal bloom during fast growth stage. Under
favorable conditions, bacteria could deliver large amount of CO2 in
a supersaturated state (Kuentzel, 1969). From our previous study,
the microalgae strain used in this study could grow well in
organic-rich wastewater with mixotrophic mode to achieve high
biomass concentration and high lipid content simultaneously