# Exploring an Integrated Manure-Sewater System for Sustainable Cyanobacterial Biomass Production
## 4 Discussion
### Growth Response of Cyanobacterial Strains HSaC and LC to Manure and Seawater Media  
The pH of cow manure, chicken manure and pig manure media before cyanobacterial culture were not similar (Figure 4). This difference in pH could be mainly dependent on the feed that the animals consume and the acidic ion concentration in the manure. Chicken (poultry) manure is rich in N [26], which contributes to acid formation. After the culture had grown for 21 days, the pH increased in the cow manure compared to the pH pre-culturing, while no change in the chicken manure and little change in the pig manure was observed. The increase in pH has a direct relationship to the growth of the cyanobacteria, because they utilize more CO\({}_{2}\) for photosynthesis, which can be used as a substrate for carbonic acid production and lowering the pH value. [PERSON] et al. [37] reported that determining the pH of growth culture media could be an indirect way to determine the potential cell growth of _Spirulina platensis_. Cow manure with 10 dS/m diluted seawater showed the highest biomass production among all treatments (Figure 5). The higher biomass production in all treatments of cow manure-seawater than in chicken and pig manure treatments might be due to the optimum macro and micro nutrient distribution in cow manure. The biochemical analysis of anaerobic digester effluent from cattle waste product has shown the existence of micronutrients that sustainably support the growth of cyanobacteria [22]. [PERSON] et al. [8] stated that most animal wastes such as livestock manure contain the essential nutrients to provide productive microalgal growth, and can be used as economically feasible algae growth media. [PERSON] et al. [9] reported that, when the loading rate of anaerobically digested cow manure effluent increased, the productivity of algal biomass increased significantly to up to 16.5 g dry weight m\({}^{-2}\) d\({}^{-1}\), however, although the loading rate of anaerobically digested pig manure effluent increased, the productivity of algal biomass remained less than 10 g dry weight m\({}^{-2}\) d\({}^{-1}\). Increased antibiotic concentrations in the pig and poultry manure could be another reason for the low biomass yield from pig and poultry manure compared to cow manure. This idea is supported by [PERSON] et al. [38] who stated that soil treated with pig manure and poultry manure resulted in a high antibiotic resistance genes (ARGs) content compared to that in cow manure and a control. In this current study, the biomass from cow manure-seawater media is higher than or equal to the biomass from the BG11 (reference cyanobacterial growth medium). In another experiment, [PERSON] et al. [22] grew different chlorella strains of microalgae in 10% anaerobic digester effluent, which was obtained from cattle manure, and this growth was compared with the growth of algae cultured in [PERSON]'s Basal Medium. The results confirmed that the biomass produced from chlorella strains in anaerobic digester effluent of cattle manure was similar to or greater than 280 mg/L, which was the amount produced in Bold's Basal Medium in 21 days. In the current study, although pig and poultry manure suppressed cyanobacterial growth, they have performed well in other experiments for microalgal biomass production. [PERSON] et al. [11] conducted an experiment on the growth of four microalgae strains, including chlorella in anaerobic digestion effluent (ADE) from poultry waste. The authors reported increased biomass production from the ADE, which resulted in high levels of protein (39% _w/w_) and carbohydrate (22% _w/w_). The report of [PERSON] et al. [39] explained that the extract of poultry litter hasthe capacity to yield up to 180% more algal biomass as compared to artificial fertilizer growth medium. Effluent with reduced phosphorous and nitrogen content yielded increased fatty acid content (7.5-11%) and biomass production of chlorella species, even though fermented pig manure with various chemical additions was used as the substrate [24].