Microalgae for municipal wastewater nutrient remediation: mechanisms, reactors and outlook for tertiary treatment

Figures & data

Figure 1. Schematic diagram of a microalgal cell summarising the biochemical pathways of nitrogen and phosphorus remediation, including indirect mechanisms (highlighted within a dashed box). © Represents co-transportation.

Table 1. Ammonium and phosphorus removal by microalgal cultures for varying waste streams.

	Design parameters		Test conditions		Influent conc. (mg L^−1)		Removal efficiency (%); Uptake rate
Algae Concentration	HRT (d); Flow velocity; Scale (m^3)	Aeration	Test waters; Temp. (°C); pH	Irradiance (µmol m^−2 s^−1)^a; Day length (h)		TP		TP	Specific growth rate (d^−1); Effluent pH	References
Chlorophyceae
Botryococcus braunii	9 Batch	50 mL min^−1 CO2	Secondary effluent	–	0.17	0.04	99.9^b	75.0	–	[35]
–	0.003		–	–			–	–	–
			7.6
Botryococcus braunii	7 Batch	50 mL min^−1 CO2	Secondary effluent	–	<0.1	0.39	99.8^b	97.4	–	[35]
–	0.003		–	–			–	–
			7.7
C. vulgaris	9 Batch	–	Wastewater effluent	100.8	7.7	0.9	55.8	–	–	[36]
253 mg L^−1	–		–	16			–		∼10
			7
C. vulgaris	2 Batch	Air bubbling	Wastewater effluent	135	–	–	74.3	70.2^d	0.186	[37]
–	0.0025		25	–			0.134 µg h^−1·10^−6cells	0.134 µg h^−1·10^−6cells	9.0–9.5
			–
C. vulgaris	9 Batch	Air bubbling	Agro-industrial wastewater	60	–	–	–	55.0^d	–	[38]
2 × 10^6 cells mL^−1	0.002		20	–				–
			–
C. vulgaris	10 Batch	0.5 v.v.m filtered air	Primary settled sewage	58^a	35.5	3.9	74.1	63.8	0.274	[31]
5 × 10^5 cells mL^−1	–		24 7.1	16			–	–	–
C. vulgaris	10 Batch	0.5 v.v.m filtered air	Primary settled sewage	58^a	35.5.	3.9	97.8	87.0	0.277	[31]
1 × 10^6 cells mL^−1	–		24	16			–	–	–
			7.1
C. vulgaris	10 Batch	0.5 v.v.m filtered air	Primary settled sewage	58^a	35.5	3.9	89.7	66.1	–	[31]
5 × 10^6 cells mL^−1	–		24	16			–	–
			7.1
C. vulgaris	10 Batch	0.5 v.v.m filtered air	Primary settled sewage	58^a	35.5	3.9	99.9	78.7	–	[31]
1 × 10^7 cells mL^−1	–		24 7.1	16			–	–
			7.1
Scenedesmus dimorphis	9 Batch	Air bubbling	Agro-industrial wastewater	60	–	–	–	55.0^d	–	[38]
2 × 10^6 cells mL^−1	0.002		20	24			–	–
			–	24
S. obliquus	7.9 Batch	160 mL min^−1	Wastewater effluent	152^a	27.4	11.8^a	94	98.0	0.686	[39]
14 mg L^−1 (dm)	0.001		20 9.3	24			–	–	–
S. obliquus	7.9 Batch	160 mL min^−1	Wastewater effluent	152^a	27.4	11.8^a	99	98.0	0.768	[39]
14 mg L^−1 (dm)	0.001		25 9.3	24			–	–	–
S. obliquus	7.9 Batch	160 mL min^−1	Wastewater effluent	152^a	27.4	11.8^a	99	94.0	1.051	[39]
14 mg L^−1 (dm)	0.001		30	24			–	–	–
			9.3
S. obliquus	7.9 Batch	160 mL min^−1	Wastewater effluent	152^a	27.4	11.8a	79	54.0	0.458	[39]
14 mg L^−1 (dm)	0.001		35 9.3	24			–	–	–
S. obliquus	2.1 Batch	Air bubbling	Wastewater effluent	135	32.5	2.5^a	100^c	60.0	0.285	[37]
–	0.0025		25	–			0.180 µg h^−1·10^−6cells	0.036 µg h^−1·10^−6cells	9.0–9.5
			–	–
Cyanobacteria
P. bohneri	5 Batch	0.1 v.v.m	Secondary effluent	–	–	–	–	–	0.190–0.490	[40]
100 mg L^−1 (dm)	0.02		–	–			2.4–19.9 mg L^−1 d^−1	1.6–13.8 mg L^−1 d^−1	8.5–11.1
			–

^a Irradiance units converted to µmol m⁻² s⁻¹ using conversion guidelines within.[41]

^b Total nitrogen.

^c Nitrate.

^d Orthophosphate

(dm) Dry mass.

Figure 2. Categories of microalgal bioreactors for wastewater remediation.

Table 2. Summary of microalgal bioreactor designs, operating parameters and performance.

Solution	Configuration	Scale	Algal biomass concentration dry mass (g L^−1)	Algal community	HRT (d)	References
HRAP	Raceway pond	Full	0.3–1.0	Mixed	4–10	[11,42,71,72]
PBR	Tubular	Pilot	1.0–2.0	Mono	1–7	[11,73,74]
	Panel	Lab			2–5
Biofilms	Floway	Full	130(g m^−2)	Mixed	6–16	[6,59,75–77]
	Submerged	Pilot			6
Matrix-immobilization	Packed bed	Lab	0.9–3.3	Mono or mixed	0.2–3	[49,78,79]

Figure 3. Influent concentration versus effluent concentration for (a) ammonium and (b) phosphate; and treatment period versus remediation efficiency for (c) ammonium and (d) phosphate for all bioreactors. HRAP (▪), biofilms (◊), matrix-immobilization (▴), PBR (○) and parity line (- -).

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