Table 5 .
Seaweed’s role in removing heavy metals, phosphorus, and nitrogen from wastewater
| Category | Seaweed type | Wastewater source | Treatment conditions | Contaminants | Treatment efficacy | References |
|---|---|---|---|---|---|---|
| Red seaweed | Gracilaria lemaneiformis | Aquaculture |
Cage co-culturing seaweed with the fish Pseudosciaena crocea Water salinity: 26–29 pH: 7.43–7.83 Temperature:18.4–26.0 °C Time: 20 days |
Phosphate and nitrogen |
Nitrogen: 21.0% Phosphate: 28.6% |
Wei et al. (2017) |
| Gracilaria chouae | Aquaculture |
Co-culturing seaweed with Sparus macrocephalus (black sea bream) Temperature: 16.61–22.68 °C Water salinity: 28.33–31.07 Time: 28 days pH: 8.16–8.2 |
Phosphate and nitrogen |
Nitrogen: 41.2% (nitrate-nitrogen: 37.76%, nitrite-nitrogen: 36.99%, ammonia–nitrogen: 29.27%) Phosphorus: 46.2% (Phosphate–phosphorus: 40.64%) |
Wu et al. (2015) | |
| Gracilaria tikvahiae | Shrimp wastewater |
Co-culturing seaweed with Litopenaeus vannamei (Pacific white shrimp) Temperature: 18–33 °C Salinity: 30.4–34.8 g/kg Time: 18 days pH: 7.4–7.9 |
Nitrogen | Nitrogen: 35% | Samocha et al. (2015) | |
|
Agarophyton tenuistipitatum Hydropuntia edulis |
Brackish water |
Temperature: 27–30 °C Salinity: 20% Seaweed biomass density: 0–4.5 g/litres pH:7.75–8.19 Time: 0-2 h hours |
Nitrogen and Phosphorus |
Optimal removal at 3.5 g/litres (ammonia–nitrogen > 80% Phosphate phosphorus removal > 20%) |
Sarkar et al. (2020) | |
| Gracilaria lemaneiformis | Seawater | Temperature: 20 ± 2 ℃, salinity: 30 ± 0.2, irradiance: 80 micromole/(cubic metre/second) with a photoperiod of 12-h light: 12-h dark. Time: 3 days | Nitrogen and Phosphorus | Ammonia–nitrogen (45.99–59.79%, nitrate-nitrogen (13.10–30.21%), nitrite-nitrogen (12.88–14.11%), and phosphate-phosphorus (27.07–31.49%) | Duan et al. (2019) | |
| Gracilariacorticata | Aqueous solution | Metal concentration: 50 mg/l, pH 5, adsorbent dosage: 104 g/l, temperature: 29.9 °C | Cobalt | Cobalt: 87.8% | Raju et al. (2021) | |
| Brown seaweed | Turbinaria ornata | Municipal wastewater | Metal concentration: 99.8 mg/l, mixing speed: 250 rounds per minute, adsorbent dosage: 16.2 g/l | Lead | 99.80% | Al-Dhabi and Arasu (2022) |
| Sargassum sp. | Simulated wastewater |
Biomass size: 2.2 millimetre Dosage: 0.1 g Temperature: 30 °C pH: 5 Time: 4-h (nickel (ii) ion) and 6-h (copper (ii) ion |
Nickel (ii) ion and copper (ii) ion | Copper (ii) ion: 2.06 mmol/gram nickel (ii) ion: 1.69 mmol/gram | Barquilha et al. (2017) | |
| Sargassum sp. | Synthetic wastewater |
Time: 60 min Temperature: 25 °C cadmium (ii) ion Seaweed: 0.5 g Rounds per minute: 150 pH: 4 Metal concentration: 5 mg/l zinc (ii) ion Biomass: 1 g pH: 3 Rounds per minute: 200 Ions concentration: 5 mg/l |
Cadmium (ii) ion and zinc (ii) ion | Cadmium (ii) ion: 95.3% zinc (ii) ion: 90.3% | Mahmood et al. (2017) | |
| Sargassum filipendula | Simulated wastewater | Sorbent size: 0.737 mm Sorbent: 2 mg/l Temperature: 25 °C Rounds per minute: 180 Time: 24 h pH: 3.5 Metal concentration: 1 mmol/l | Silver, cadmium, chromium, copper, nickel, lead, and zinc ions | Silver: 33.62% Cadmium: 78.03% Chromium: 72.8% Copper: 69.05% Nickel: 32.74% Lead: 56.19% Zinc: 44.21% | Cardoso et al. (2017) | |
| Sargassum dentifolium | Simulated wastewater | Sorbent dosage: 1.5 g/ 100 ml, Ion concentration: 100 parts per million, the flocculation contact time was 1 h followed by 12 h static, temperature: 50 °C, pH: 7 | Chromium | Chromium (VI): 99.68% | Husien et al. (2019) | |
| Cystoseira crinite and Cystoseira barbata | Aqueous and wastewater solutions | Chromium (III): Dosage: 100 parts per million, pH 4.5, contact time: 120 min, adsorbent dosage: 0.1 g/50 ml. Chromium (VI): Ion concentration: 100 parts per million, adsorbent dosage: 100 mg/50 ml, contact time: 24-h, pH: 2.0 | Chromium (III) and Chromium (VI) | Chromium (III): 73.34% (Cystoseira crinite), 70.70% (Cystoseira barbata) Chromium (VI): 28% (Cystoseira crinite) 35%, (Cystoseira barbata) | Yalcin and Ozyurek (2018) | |
|
Seaweeds Ulva intestinalis, Gracilaria sp., Fucus spiralis, Osmundea pinnatifida, Ulva lactuca, Fucus vesiculosus |
Synthetic seawater | Metal concentration: 1 micromole per cubic decimetre, 72 h contact time, temperature: 22 °C, pH: 8.5, salinity of 30 g per cubic decimetre | Mercury |
95% 90% 85% 80% 90% 80% |
Fabre et al. (2020) | |
| Sargassum muticum | Mining-influenced water | Metal dosage: 2.5 mg/l, temperature: 293 Kelvin, pH: 7 | Arsenic | Almost 100% | Vieira et al. (2017) | |
| Caulerpa scalpelliformis | industrial wastewater |
Adsorbent dosage: 1.5 g/litre, temperature: 30 °C contact time: 1 h, pH: 5.7 Agitation: 150 rounds per minute |
Zinc | 83.3 mg/gram | Jayakumar et al. (2021) | |
| Sargassum polycystum | Simulated water | Cadmium: Adsorbent dosage: 1.8 g/l, pH: 4.65, agitation speed: 76 rounds per minute Zinc: pH: 5.7, agitation speed: 125 rounds per minute. adsorbent dosage: 1.2 g/l | Multi-metals | Cadmium: 86.20 Zinc: 92.90% | Jayakumar et al. (2022) | |
| Sargassum filipendula | Real and synthetic effluents |
Metal concentration: 1 mmol/l (19.56 mg/l of nickel; 17.33 mg/l of chromium; and 21.79 mg/l of zinc) Temperature: 50 °C |
Multi-metals | Chromium: 0.864 mol/g Zinc: 0.302 mmol/g Nickel: 0.347 mmol/g | Costa et al. (2020) | |
| Green seaweed | Ulva rigida | Simulated wastewater | Temperature: 20 °C Sorbent: 0.5 g Sorbent size: 0.5 cm Time: 5 h Rounds per minute: 180 Metals concentration: 25 mg/l | arsenic cation (3 +), arsenic cation (5 +), antimony (3 +) selenium (4 +) ions and selenium (6 +) ions | Selenium: (4 +) ions: 0.5 mg/g (pH: 2–4) Selenium: (6 +) ions: 0.2 mg/gram (pH: 2–3) Limited removal efficiency towards arsenic but was effective for antimony and selenium | Filote et al. (2017) |
Seaweeds demonstrated a great capacity for removing nutrients from wastewater. For instance, seaweeds can absorb over 41% of nitrogen and phosphorus. In addition to nitrate-nitrogen, ammonia–nitrogen, and nitrite-nitrogen, seaweeds can also remove other nitrogen forms. Similarly, seaweeds can absorb a variety of heavy metals, including copper, cobalt, iron, zinc, lead, nickel, cadmium, silver, chromium, arsenic, antimony, and mercury. This makes seaweeds a very promising option for wastewater treatment on a large scale