Introduction
Grey water is wastewater generated from domestic activities such as bathing, washing, laundry and other non-toilet household activities. It contains organic matter, nutrients, suspended solids and other dissolved substances. Conventional treatment methods can require considerable infrastructure and operational inputs. Biological treatment using algae is an alternative approach in which algae can utilize nutrients and organic components from wastewater while growing under suitable environmental conditions.
The present experiment was conducted to study the potential of naturally collected freshwater algae for grey water treatment. Three different algal samples were collected from different freshwater locations and evaluated for their growth and their potential to improve grey water quality.
Objective
The main objectives of this experiment were:
- To collect different naturally occurring freshwater algae from different locations.
- To maintain the collected algae in normal water as a reference/mother culture.
- To evaluate the performance of the algae in grey water.
- To study changes in important grey water parameters such as:
- COD
- pH
- TDS
- EC
- To observe algal growth and physical changes in grey water during treatment.
- To compare the response of different algal samples to grey water.
- To evaluate duckweed as an additional biological treatment option.
- If direct algal treatment does not provide satisfactory results, to evaluate further cultivation/conditioning of algae using BG-11 medium.
Why are Algae Used for Greywater Treatment ?
Microalgae naturally utilize nutrients present in wastewater for their growth.
During photosynthesis, algae:
- Absorb nitrogen and phosphorus
- Consume carbon dioxide (CO₂)
- Produce oxygen (O₂)
- Increase dissolved oxygen in water
- Support aerobic bacteria that degrade organic pollutants
Microalgae use sunlight, carbon dioxide (CO₂), water, and nutrients present in greywater for photosynthesis and growth. During this process:
Algae absorb nitrogen and phosphorus, reducing nutrient pollution.
They release oxygen, which supports aerobic bacteria.
Aerobic bacteria degrade organic pollutants, lowering BOD and COD.
Algal biomass can be harvested and used as biofertilizer or biofuel feedstock.
Pollutants Removed
1.Organic matter (reduces BOD and COD)
2. Nitrogen compounds (NH₄⁺, NO₃⁻)
3. Phosphates
4. Suspended solids
5. Some heavy metals
6. Pathogenic microorganisms (partially)
Collection of Algal Samples
Three different algal samples were collected from freshwater sources.
Sample 1 – Flowing Water
The first algal sample was collected from a flowing freshwater body. The algae were collected from the surface level of the water.
Sample 2 – Well Water
The second algal sample was collected from a well. The naturally occurring algal biomass present in/around the water surface was collected.
Sample 3 – Pond Water
The third algal sample was collected from a pond. The algae were present at the surface level of the pond and were harvested for laboratory evaluation.
Sample Coding
For systematic experimentation, the samples can be coded as:
| Sample | Source | Sample Code |
|---|
| Algae from flowing water | Flowing freshwater body | A1 |
| Algae from well | Well water | A2 |
| Algae from pond | Pond water | A3 |
The exact species identification of these samples was not confirmed at this stage. Therefore, they are referred to as Algal Sample A1, A2 and A3 until microscopic/molecular identification is performed.
Laboratory Processing of Algal Samples
The collected algal samples were brought to the laboratory for further experimentation.
The samples were initially examined and maintained separately to avoid mixing of the three algal populations.
Preparation of Mother Culture / Reference Culture
A portion of each collected algal sample was maintained in normal water under laboratory conditions.
This setup was maintained as a reference/mother culture to observe the normal growth behaviour of the algae in comparatively non-wastewater conditions.
The purpose of this setup was to compare:
Normal water + algae with Grey water + algae
This comparison will help determine whether any reduction in algal growth in grey water is associated with the wastewater conditions.
Grey Water Used for the Experiment
Grey water collected from the campus source was selected for the treatment experiment. The initial COD of the grey water was approximately 280 mg/L.
Before the addition of algal biomass, the grey water was characterized by measuring COD, pH, TDS and EC.
For the treatment experiment, 4 L of grey water was transferred into each transparent rectangular container. A 3 g biomass of each algal sample (A1, A2 and A3) was separately added to the respective containers. Aeration was provided through bubbling throughout the experimental period.
Duckweed Treatment Setup
In addition to the algae experiment, a separate biological treatment setup was prepared using duckweed.
The same type of transparent rectangular container was used.
Duckweed Setup
Grey water volume: 4 L
Duckweed biomass: 1 g
Container: Transparent rectangular tub
Treatment organism: Duckweed
Observation: Growth and survival of duckweed in grey water
The duckweed setup will be monitored to determine whether duckweed can survive and grow under the given grey water conditions.
The following parameters can also be monitored: Duckweed growth, Biomass increase,Colour ,Root development, Water colour, pH,EC, TDS,COD.
Comparison Table
| Parameter | Algae A1 | Algae A2 | Algae A3 | Duckweed |
|---|---|---|---|---|
| Initial Growth (Biomass ) | 3 gm | 3 gm | 3 gm | 1 gm |
| Growth (Biomass ) | ||||
| Initial COD | 300 mg/L | 300 mg/L | 300 mg/L | 300 mg/L |
| Final COD | ||||
| COD Removal % | ||||
| Initial pH | 8.62 | 8.62 | 8.62 | 8.62 |
| Final pH | ||||
| Initial EC | 484 mS/cm | 484 mS/cm | 484 mS/cm | 484 mS/cm |
| Final EC | ||||
| Initial TDS | 242 ppm | 242 ppm | 242 ppm | 242 ppm |
| Final TDS |
5 Sept 2026
Grey Water Treatment Using Algae and Duckweed – Progress & Next Steps
- Initial Experimental Setup
Grey water was collected and characterized using different water-quality parameters such as pH, EC, TDS and COD. The initial COD was approximately 300 mg/L. Different freshwater algae samples were introduced into grey water under controlled conditions with artificial light and continuous aeration (bubbling).
2. Observation with Direct Grey Water Treatment
When algae were directly introduced into untreated grey water, significant stress was observed. The algal biomass gradually deteriorated, with apparent cell damage and pigment release, resulting in the grey water becoming dark red/orange to reddish-brown. In comparison, algae maintained in tap water under similar light and aeration conditions did not show the same deterioration. This indicated that the grey water composition was adversely affecting algal survival.
3. Modification of Algae Treatment Strategy
Based on experimental observations and discussion with Dixit Sir , direct application of algae to raw grey water was considered unsuitable. Therefore, the next phase will use diluted grey water to reduce the initial stress on algae.
For example, a 50% dilution will be prepared using:
- 2 L grey water
- 2 L clean tap water
- Final volume: 4 L
The diluted grey water will then be treated with algae under the same controlled light and aeration conditions. Water-quality parameters and algal condition will be monitored to evaluate treatment efficiency.
4. Duckweed Observation
In parallel, duckweed (Lemna sp.) was evaluated in grey water. Unlike the algae, duckweed did not show visible signs of severe deterioration. Instead, it showed growth in grey water, suggesting that it may utilize available nutrients and organic-associated nutrients in the water for biomass production while contributing to reduction of the wastewater load.
5. Current Work
At present:
- The algae treatment experiment is continuing using diluted grey water.
- Light and aeration are being maintained under controlled conditions.
- Changes in pH, EC, TDS, COD and algal appearance will be monitored.
- The duckweed trial is being continued to evaluate its growth and grey water treatment potential.
6. Next Steps
The next phase will focus on a systematic duckweed treatment trial. Its growth, biomass production and effect on grey water quality will be evaluated by monitoring parameters such as COD, pH, EC and TDS before and after treatment.
The overall objective is to compare the performance of algae and duckweed and identify a suitable biological approach for effective grey water treatment.
