Research Of Large-scale Microalgae Culturing To Purity Biogas Slurry

With the rapid development of breeding industry, livestock and poultry manure fermentation produce a large amount of biogas slurry, it’s a serious threat to the natural environment. Microalgae is an important producers in the ecosystem, with the mature of culturing microalgae technology, the use of sewage for large-scale microalgae culture can save the microalgae culture cost and realize waste recycling, at the same time, can realize the purification of the sewage and protect water sources.The new wastewater treatment technology with microalgae on the basis of their economic, environmental protection, cover a small area and strong operability advantages shows its great charm and application value.This paper on the basis of the small scale of microalgae purified biogas slurry test, use the tubular photobioreactor and the raceway pond to enlarge the microalgae culture, launched the research from the following aspects:(1) Researched on the growth of Chlorella pyrenoidosa and the removal of nitrogen and phosphorus nutrients in the biogas slurry in laboratory-scale. Chlorella pyrenoidosa was isolated from biogas slurry. With the experiment of pollution resistant, chlorella pyrenoidosa was able to adapt to the environment of biogas slurry and grow rapidly. Total nitrogen, total phosphorus removal effect in 50%,75%,100% concentration of biogas slurry was very good. After eight days cultivation, the total nitrogen content in the above three biogas slurry concentration were 16.69 mg/L,16.21 mg/L and 18.26 mg/L, removal rate were 84.84%,90.11% and 91.50% respectively; Total phosphorus content were 1.54 mg/L,1.06 mg/L and 1.26 mg/L, the removal rate were 88.55%,91.56% and 93.27% respectively. The results showed that the pollutant removal ability of Chlorella pyrenoidosa was higher, and has the potential for large-scale application.(2) Studied on Chlorella pyrenoidosa cleaned 50%,75%, biogas slurry in tubular photobioreactor. With the treatment of Chlorella pyrenoidosa, nitrogen and phosphorus removal rates were 36.64% and 33.42% respectively in 50% concentration of biogas slurry, and 46.88% and 57.81% respectively in 75% concentration of biogas slurry.In this experimental, Chlorella pyrenoidosa grew slowly in the tubular photobioreactor, removal rate of N and P in biogas slurry was also low. The capacity of Chlorella pyrenoidosa remove the nutrients in high concentration sewage was low.(3) Established a biogas slurry pretreatment system. The system removed most of the biogas slurry particles, reduced the biogas slurry turbidity and nutrients. In the experiment of Chlorella pyrenoidosa purified 50% biogas slurry, the biogas slurry total nitrogen content was 254.20 mg/L, total phosphorus content was 108.25 mg/L, with the pretreatment of the system total nitrogen content was 51.55 mg/L, total phosphorus content was 45.28 mg/L. In the experiment of Chlorella pyrenoidosa purified 75% biogas slurry, the biogas slurry total nitrogen content was 420.63 mg/L, total phosphorus content was 60.41 mg/L, after pretreatment, the total nitrogen content was 248.08 mg/L, total phosphorus content was 15.36 mg/L. Pretreatment of biogas slurry can remove 79.72%, 58.17% and 42.92%,74.57% of the total nitrogen and total phosphorus respectively. After pretreatment, the turbidity of biogas slurry was low, color changed from black to clear brown, light permeability was enhanced, and the surface have no obvious plankton, the nutrient concentrations were decreased. After inoculation, microalgae can quickly adapt to the wastewater environment.(4) Researched on Chlorella pyrenoidosa cleaned 50%,75% concentration of biogas slurry in the raceway pond. In the experiment of Chlorella pyrenoidosa purified 50% biogas slurry, in the first three days after inoculation, total nitrogen and total phosphorus content decreases were noticeable, total nitrogen content was 11.89 mg/L, total phosphorus content was 7.61 mg/L, the removal rate were 69.74% and 66.38% respectively. In the experiment with 75% concentration of biogas slurry, in the first three days after inoculation, total nitrogen and total phosphorus content decreased significantly, total nitrogen content was 14.18 mg/L, total phosphorus content was 2.42 mg/L. After that removal rate of chlorella pyrenoidosa nitrogen was slow down, the lowest total nitrogen was 8.07 mg/L. Total phosphorus content reached the lowest 2.03 mg/L in the fourth day. The removal rate of total nitrogen and total phosphorus were 95.51% and 85.32% respectively. After the treatment with Chlorella pyrenoidosa, the biogas slurry can reach the secondary emission standard of breeding pollutant.(5) Analysed the feeding value of Chlorella pyrenoidosa powder growing in the biogas slurry. The crude protein, fat, ash content, chlorophyll a and lutein of Chlorella pyrenoidosa were accounted for 62.56% 5.20%,5.76%,5.20% and 5.76% of the dry weight of the algae cells,and Chlorella pyrenoidosa contained a variety of mineral elements and amino acid. Chlorella pyrenoidosa has great potential for development of high quality protein feed.