Black water recycling system by using different treatments on bio-beds

Black water is wastewater from toilets and is contaminated with disease carrying bacteria. It requires adequate handling as it can generate environmental disturbances and serious health problems to human and aquatic life. These impact begins when blackwater contaminate raw water sources used for daily basis. So, black water must be processed before discharging it into river. Generally, it is stored into septic tank or directly channeled to the sewage system and then processed into treatment plant.

In this study, blackwater treatment is performed by using different systems. The observation is focused on decrease in Chemical Oxygen Demand (COD) during processing. COD is the amount oxygen required to decompose the organic matter. Also, sustainability of plants in black water is to be observed.

Objectives

1. To compare the three systems used for treatment –
   • Flood and drain system
   • System with bubbler
   • system without bubbler
2. To check the effect of black water on plant growth

06/04/2022 – 07/04/2022

Selection of plant

After discussion, plants like water hyacinth, Canna Indica are selected. This plants can absorb pollutants and can provide suitable environment for aerobic bacteria to remove various impurities.

Collection of black water

Firstly, for collecting black water a tank is placed at drainage outlet of girls hostel, which is primarily treated in K.K.Nag’s Bio-digester. On second day, water was collected in the tank.

07/04/2022-08/04/2022

Determination of COD

Chemical oxygen demand is amount of dissolved oxygen that must be present in water to oxidize chemical organic materials. The initial COD of black water is needed to determine. Sample for determining COD collected from collected black water in the tank. The procedure used for it by using COD digester is as follows:

Materials for COD test

1. Potassium dichromate (K₂Cr₂O₇).
2. Mercuric sulphate (HgSO4)
3. Sulfuric acid (H2SO4)
4. Ferrous ammonium sulphate (FAS)
5. Ferron indicator
6. Potassium hydrogen phosphate (KHP)
7. 250 ml Erlenmeyer flask
8. Reflux condenser
9. COD tubes
10. Measuring cylinder
11. Analytical balance
12. COD tube stands
13. Hand gloves

Preparation of chemicals

1. Preparation of 0.25 N potassium dichromate solution: –
   12.25 gm. potassium dichromate powder dissolved in 1000 ml distilled water in 1000
   ml volumetric flask.
2. Preparation of Ammonium Ferrous Sulphate solution: –
   24.5 gm. Ammonium Ferrous sulphate powder dissolved in 250 ml distilled water in
   250 ml distilled water in 250 ml volumetric flask. Add 5ml Sulphuric acid.
3. Preparation of Potassium Hydrogen Phosphate solution: –
   0.425 gm. of dried KHP powder dissolved in 1000 ml distilled water in 1000 ml
   volumetric flask. (Dried this powder for 2 hours in oven)

Procedure

1. Took 0.4 gm. AgSo4 (silver sulphate) in COD tubes.
2. Added 20 ml sample in each COD tube.
3. Added 20 ml distilled water in each COD tube.
4. Added stones (crush on beads) 1 or 2 pieces.
5. Added 10 ml (0.25 N) K2Cr2O7 Potassium dichromate solution.
6. Added 30 ml conc sulfuric acid slowly along with swirling.
7. If the solution turns green more known quantities of K2Cr2O7 solution is needed to add.
8. Kept COD tubes in COD apparatus to digest the sample..
9. Attached the condenser & set 150 Degree Celsius temperature.
10. Kept for 2 hours filled COD tubes in COD apparatus for 150 degree Celsius.
11. After 2 hours switched it off & removed COD tubes & cooled sample for room temperature.
12. Took the above sample in a conical flask. Added 150 ml distilled water.
13. Titration: – Titrated above solution with 0.1 N FAS (ferrous ammonium sulphate) solution by using Ferron indicator (add 3-4 drops). The end point of this titration is blue green to reddish brown.

Formula of COD

COD = {(a-b) X N X 8000}/ml of sample solution
Where,

1. A-Reading blank solution.
2. B-Reading with sample solutions
3. N- Normality of FAS solution

Dilution factor = ( ml of sample + distilled water )/ ml of sample

Calculation of COD

Sample	Readings	COD (mg/lit)
Blank	10.4	–
KPH	4.6	529
Black water	8.1	2340
Grey water	8.9	612

Sample	Readings	COD (mg/lit)
Blank	10.1	–
Tap water	9.5	61.2
Black water	8.5	1632
Grey water	9.4	714

The sample of grey water and black water is diluted with distilled water and dilution factor is considered in calculation. On first day, sample of grey water was collected from grey water system near Dixit Sir’s house and on second day, it was collected from grey water system near the food lab. The COD of black water is 2340 mg/lit and we have to reduce it.

06/04/2022-10/04/2022

Collection of material

The material required for setup of systems for treatment of black water is as follows:

1. Buckets
2. Bubbler
3. Stand
4. Lateral
5. T-joint
6. Elbow
7. Grommet
8. wires
9. ARDUINO
10. Sub-mersible pump 18 watt

11/04/2022-25/04/2022

Bill of material

After calculating the initial COD, the set-up of all systems i.e. bubbling and without bubbling, flood and drain is done.

• Bubbling system: In this system, bubblers are used which will aerate the water and provide oxygen to bacteria which will further decompose organic matter. The two buckets are used in which 17 litres of black water is filled. In first bucket, water hyacinth is planted and in second indian shot is planted.
• Without bubbling system: This system is same as bubbling system. Only difference is bubblers are not used.

• Flood and drain system: In this system, the bacteria will get more space to grow and the media used i.e. bricks will also give some nutrients for growth of bacteria. Contact of bacteria with air will be more as water will flood and drain after fixed time of interval. The setup is using two buckets and two reservoirs.. Buckets are placed on stand and reservoirs are under the stand.The bucket in which Indian shot is planted is connected with drip pipe at bottom. Hence, the black water will drain out from bottom. And the bucket in which water hyacinth is planted is connected with drip pipe at a height of 5 cm from side. This drip pipes are connected with submersible pumps. A timer is used for this system and the interval is set for every 30 minutes.. Both pumps used are operating on single arduino timer.

Block diagram

Arduino Program for setting timer

int relay1 = 4;
int relay2 = 5;

void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
pinMode (relay1, OUTPUT);
pinMode (relay2, OUTPUT);
}

void loop() {
// put your main code here, to run repeatedly:
digitalWrite(relay1,LOW);//relay on
digitalWrite(relay2,LOW);
delay(110000);//1 MIN 83SEC
digitalWrite(relay1,HIGH);//relay off
digitalWrite(relay2,HIGH);
delay (1800000);//30MIN
}

25/04/2022

Observations of COD(1^st trial)

	without bubbler	with bubbler	flood and drain
Initial COD (day 1) (mg/lit)	2340	2340	2340
Initial COD (day 1) (mg/lit)	1632	1632	1632
After 17 days (mg/lit)	1830	2142	1326

Due to unavailability of chemicals the COD is determined after 17 days. It is needed to determine after fixed days of interval to see the effect of different systems and plants.

30/04/2022

Trial 2^nd

The three systems of black water were setup on different times and the results cannot be compared effectively. So, the systems are set again at same time. For this, the black water in previous systems is mixed and used.

29/04/2022 – 31/05/2022

Observations of COD

	Without bubbler (Water hyacinth)	Without bubbler (Indian shot)	With bubbler (Water hyacinth)	With bubbler (Indian shot)	Flood and drain (Water hyacinth)	Flood and drain (Indian shot)
Initial COD (mg/lit) 30/04/2022	918	918	918	918	918	918
03/05/2022	714	714	714	510	510	306
06/05/2022	612	510	510	408	306	204

For 3^rd trial, black water is collected again and distributed in system on 10/05/2022. The COD of this water is 2244 mg/lit.

	Without bubbler (Water hyacinth)	Without bubbler (Canna Indica)	With bubbler (Water hyacinth)	With bubbler (Canna Indica)	Flood and drain (Water hyacinth)	Flood and drain (Canna Indica)
Initial COD (mg/lit) 11/05/2022	2244	2244	2244	2244	2244	2244
14/05/2022	2193	2193	2193	2142	2040	1836
17/05/2022	2040	1836	1785	1428	1530	1224
20/05/2022	1938	1632	1428	1122	1122	918
23/05/2022	1836	1326	1224	918	816	408
26/05/2022	1785	1122	918	612	510	204

From the observations of trial taken, it is seen that the sustainability of water hyacinth is less in black water. It starts to wilt in 4-5 days. So in 4^th trial, it is decided to dilute the black water with tap water. For dilution following calculation is done:

	Without bubbler (Water hyacinth)	Without bubbler (Canna Indica)	With bubbler (Water hyacinth)	With bubbler (Canna Indica)	Flood and drain (Water hyacinth)	Flood and drain (Water hyacinth)
28/05/2022	2244	2244	2244	2244	2244	2244
31/05/2022	1785	1122	918	612	510	204

Result

	Without bubbler (Water Hyacinth)	Without bubbler (Canna Indica)	With bubbler (Water Hyacinth)	With bubbler (Canna Indica)	Flood and drain (Water Hyacinth)	Flood and drain (Canna Indica)
% losses in COD IN 15 days	20%	50%	59%	72%	77%	90%

Conclusion

• COD is decreased in every system. But maximum decrease in COD is found in flood and drain system compared to others.
• The system with Canna Indica plants shows better results. The COD reduces more in system with Canna Indica.
• In black water, water hyacinth was sustaining in starting period but after 4-5 days it started to wilt which can be seen from the figure 18. The growth of Canna Indica is better than water hyacinth. The roots were growing well.