Grey Water Treatment Using Algae Growth

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

Algae from well

Well water

Algae from pond

Pond water

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 30 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.

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.

The algae treatment experiment is continuing using diluted grey water.
Light and aeration are being maintained under controlled conditions.
Changes in COD and algal appearance will be monitored.
The duckweed trial is being continued to evaluate its growth and grey water treatment potential.
The next phase will focus on a 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.

10 Sept 2026 – 25 Sept 2026

Results and Observations

COD analysis was carried out to evaluate the changes in organic load of grey water under different treatment conditions. The COD values obtained from the different experimental setups were compared with the initial grey water COD.

The following results were obtained:

Sample / Treatment	Titration Value (mL)	Final COD (mg/L)	COD Reduction (%)
Grey Water +Algae from pond	12.0	244	18.67 %
Grey Water + Bubbling	16.3	72	76.00 %
Grey Water + Duckweed	15.1	120	60.00 %

The initial COD of the grey water was approximately 300 mg/L.

Algae Treatment

Among the tested algal samples, Algal Sample A3 showed a final COD of 244 mg/L, corresponding to approximately 18.67% COD reduction.

Although COD reduction was observed, the reduction was comparatively limited. This indicates that the algae were able to remain active to some extent, but the grey water conditions may have restricted algal growth and treatment performance.

Further monitoring is required to determine whether longer treatment duration or dilution of grey water can improve algal performance.

2. Bubbling / Aeration Treatment

The grey water subjected to continuous bubbling showed a final COD of 72 mg/L, corresponding to approximately 76% COD reduction.

This indicates a substantial reduction in COD during the experimental period. The observed reduction may be associated with aeration-supported biological activity and oxidation of biodegradable organic matter.

3. Duckweed Treatment

The duckweed-treated grey water showed a final COD of 120 mg/L, corresponding to approximately 60% COD reduction.

Duckweed also showed visible growth and survival during the treatment period. The reduction in COD along with continued duckweed growth indicates that duckweed has potential for further evaluation as a biological treatment option.

The increase in duckweed biomass should be measured in future experiments to establish a relationship between biomass production and pollutant removal.

Comparison of Treatment Performance :

The observed COD reduction for the three treatment conditions was compared with the initial grey water COD.

Treatment	Initial COD (mg/L)	Final COD (mg/L)	COD Reduction
Grey Water + Algae from pond	300	244	18.67%
Grey Water + Bubbling	300	72	76.00%
Grey Water + Duckweed	300	120	60.00%

The results show that COD reduction occurred under all three tested conditions, but the magnitude of reduction was different.

The experiment also demonstrated an important difference between the biological systems. Direct exposure of algae to untreated grey water resulted in visible stress and deterioration of algal biomass, whereas duckweed showed better visible survival and growth under the tested conditions.