Nutrient removal and biomass production from dairy farm liquid digestate treatment using microalga Chlorella vulgaris

doi:10.11949/j.issn.0438-1157.20180739

Abstract

Abstract:

In this study, the treatment performance of dairy farm liquid digestate by freshwater microalga Chlorella vulgaris NIES-227 was investigated and the potential of biomass utilization was evaluated. In column photobioreactors, Chlorella vulgaris was used to treat wastewaters containing unsterilized liquid digestate at concentrations of 25%, 50%, 75%, and 100%. The results showed that the removal of total nitrogen (TN), total phosphorus (TP) and COD were 36.0%—92.5%, 42.8%—100% and 6.9%—32.2%, respectively. The microalgae exhibited the maximum removal efficiencies of nitrogen and phosphorus in 25% liquid digestate, and the maximum removals of ammonia nitrogen (NH₃-N), TN and TP were 99.9%, 91.0% and 100%, respectively. The microalgae grew well in low concentrations of liquid digestate (25%—50%), and the highest biomass productivity was obtained in 50% liquid digestate with the value of 393.6 mg/(L·d). However, microalgal growth was inhibited in higher concentrations of liquid digestate (75%—100%), which led to the decreases of the removal of nitrogen and phosphorus. The number of bacteria increased significantly during the cultivation among all the treatment groups, which was beneficial to the COD removal. The contents of total lipid, total sugar and protein in biomass harvested from different concentrations of liquid digestate were 13.2%—32.2%, 12.3%—27.6% and 16.2%—30.9%, respectively. The experimental data show that low-concentration biogas slurry can produce more high-energy components of biomass, which is suitable for biofuel development; high-concentration biogas slurry can produce biomass with more protein, which is more suitable for animal feed.

Key words: Chlorella, dairy farm liquid digestate, nutrition removal, biomass production, resource utilization

摘要：

为资源化处理奶牛场沼液、探究小球藻Chlorella vulgaris NIES-227对奶牛场沼液的处理能力以及生物质利用潜力，在柱式光生物反应器中利用小球藻处理沼液占比分别为25%、50%、75%和 100% 4种不同浓度的未灭菌污水。研究结果显示，各浓度污水中总氮、总磷和COD的去除率分别为36.0%～92.5%、42.8%～100%和6.9%～32.2%。在沼液占比为25%的污水中氮磷的去除率最高，氨氮、总氮和总磷的去除效率分别可达99.9%、91.0%和100%。微藻在低浓度沼液（25%～50%）中生长状态良好，在沼液占比为50%的污水中可获得最高生物质产率393.6 mg/(L·d)。但是在高浓度沼液（75%～100%）中微藻生长受到一定抑制，导致氮磷的去除效果变差。培养期间细菌的数量增长显著，促进了COD的去除。各浓度沼液生物质中总脂、总糖和蛋白质含量分别为13.2%～32.2%、12.3%～27.6%和16.2%～30.9%。实验数据表明，低浓度沼液能产生更多高能量组分的生物质，适合用作生物燃料的开发；高浓度沼液能产生含较多蛋白质的生物质，更适合用作动物饲料。

关键词: 小球藻, 奶牛场沼液, 营养去除, 生物质生产, 资源利用

CLC Number:

Q 938

Siran FENG, Pingzhong FENG, Shunni ZHU, Zhongming WANG, Zhenhong YUAN. Nutrient removal and biomass production from dairy farm liquid digestate treatment using microalga Chlorella vulgaris[J]. CIESC Journal, 2019, 70(1): 227-233.

冯思然, 丰平仲, 朱顺妮, 王忠铭, 袁振宏. 小球藻对奶牛场沼液处理能力及生物质生产的探究[J]. 化工学报, 2019, 70(1): 227-233.

Figures/Tables 8

Table 1 Contents of COD, nitrogen and phosphorous in swine and dairy liquid digestate

Liquid digestate type	COD/(mg/L)	TN/(mg/L)	NH₃-N/(mg/L)	Phosphate/(mg/L)	Ref.
pig farm liquid digestate	1046	254	220	85.9	[8]
dairy farm liquid digestate	1480	621.1	575.4	252.7	[9]

Table 2 Water characteristics of dairy farm liquid digestate under different treatments

Digestate	pH	COD/(mg/L)	NH₃-N/(mg/L)	TN/(mg/L)	TP/(mg/L)	TSS/(g/L)
raw liquid digestate	7.15	1724	567	605	82	2.6
after stored at 4℃	7.94	1498	545	650	11.3	—
experimental liquid digestate	7.62	1446	529.5	535	77.6	0.13

Fig.1 Removal of COD(a), phosphate(b), NH3-N (c) and TN (d) in liquid digestate with different concentrations

Fig.2 Growth of biomass in different liquid digestate concentrations

Fig.3 Microalgal cell number among all cultures

Fig.4 Changes in bacterial colonies on day 0, 3 and 7 among all cultures

Fig.5 Contents of total lipid, total sugar and protein among all cultures

Table 3 Contents of N, C and H elements in biomass from different concentrations of liquid digestate

Liquid digestate concentrations/%	Elements contents/%
Liquid digestate concentrations/%	N	C	H
25	5.1	55.7	7.8
50	8.8	49.5	7.2
75	9.2	50.5	7.0
100	9.7	50.9	7.1

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