Introduction
Based on our Human Practice investigations, we have designed our hardware to be:
Thus, we have created an all-in-one system that automatically carries out the detection and bioremediation. Our hardware is divided into three necessary modules: detector chamber, purification chamber, and operating system.
Image 1. the NEZHA Hardware System
Users are firstly required to insert our detector bacteria pack (for specific heavy metal) into the detector chamber. Once the machine has started, water will be pumped from the reservoir firstly into the detector chamber, where the system will automatically assess the level of fluorescence produced showing the user whether the water sample is contaminated by heavy metal.
After the machine determines that remediation is needed, it will give a visual output of the deduced concentration of heavy metal, and the user will follow the instruction to insert the remediation bacteria pack into the remediation chamber (aka. the “filter”), and switch the valve to the “remediation” side. The machine will resume when the users are ready, and water will flow into the remediation chamber.
After water is exposed to the remediation bacteria for a period of time, the escaped bacteria and noncanonical amino acids will be filtered out in the bio-safety chamber, and the water with less heavy metal concentration will return to the reservoir.
The circular flow of water will continue until the users stop the program.
Detector chamber
This module is essentially a simplified, cheap, yet automatic version of a transilluminator optimized for water samples, which detects the level of GFP present in the sample mixed with our detector bacteria.
Image 2. Computer Rendering of the Detector Chamber
Water will enter through the bottom of the chamber under it reaches a fixed volume, and it will interact with the detector bacteria. Backflow, as well as bacteria leakage, is prevented by a unidirectional valve. After waiting for a certain period of time allowing our genetic circuit to react, the ultraviolet LED will be turned on and emit 400nm light wave which can excite GFP. If the sample contains the heavy metal the bacteria pack detects, it will emit a green light; the light-dependent resistor will record the level of fluorescence and report the hypothesized concentration of the heavy metal. To prevent the UV light being picked up by the LDR, a transparent orange acrylic film (which filters out any UV light) is attached in front of the LDR.
Image 3. Three-view Sketch of the Detector Chamber
Its prototype is printed using a 3D printer with Poly(Lactic Acid) filament. It is non-toxic, biodegradable and ensures adhesion of bacteria.
Purification chamber
This filter serves to remove the heavy metal in the water sample. Similarly, water enters from below, interacts with the bioremediation bacteria (either on or not attached on resin pellets), and flows out from the top. In this way, it maximizes the time that the bacteria are exposed to the water sample, consequently maximizing the efficiency of reaction. We have designed so that many filter cells can be aligned together in case of large-scale water treatment.
Image 4. Computer Rendering of the Purification Chamber
As a measure of biosafety, we have employed a unidirectional valve at the bottom of each cell, as well as a semi-permeable film on the top. This prevents the bacteria from escaping and causing horizontal gene transfer.
The prototype is also printed using 3D printer and PLA.
Image 5. Three-view Sketch of the Purification Chamber
Operating system
Aiming for being affordable and user-friendly, we have chosen the Arduino Uno model as the machine's microcontroller, which employs C++ and costs less than $10 each.
Logic Flowchart:
Arduino code:
#include
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
const int motp = 9 ;
const int mot_1 = 7 ;
const int mot_2 = 6 ;
const int ld = A0;
const int uv = 13;
const int swi = 8;
int i =0;
int brt = 10;
int swiSta = 0;
void setup() {
Serial.begin(9600);
lcd.begin(16, 2);
pinMode(motp,OUTPUT) ;
pinMode(mot_1,OUTPUT) ;
pinMode(mot_2,OUTPUT) ;
pinMode(ld,INPUT) ;
pinMode(uv,OUTPUT) ;
pinMode(swi,INPUT);
}
void loop() {
lcd.setCursor(0, 0);
lcd.print("Wait for");
lcd.setCursor(0, 1);
lcd.print("10 minutes");
digitalWrite(7,HIGH) ;
digitalWrite(6,LOW) ;
analogWrite(motp,75) ;
delay(5000);
digitalWrite(7,LOW) ;
digitalWrite(6,LOW) ;
analogWrite(motp,0) ;
delay(600000);
digitalWrite(13,HIGH);
lcd.setCursor(0, 0);
lcd.print(" ");
lcd.setCursor(0, 1);
lcd.print(" ");
delay(1000);
brt=analogRead(ld);
while (i<50){
lcd.setCursor(0, 0);
lcd.print("The conc. is");
lcd.setCursor(0, 1);
lcd.print(brt);
lcd.setCursor(6, 1);
lcd.print("mM");
delay(100);
brt=analogRead(ld);
i++;
}
if (brt>500){
digitalWrite(13,LOW);
lcd.setCursor(0, 0);
lcd.print(" ");
lcd.setCursor(0, 1);
lcd.print(" ");
lcd.setCursor(0, 0);
lcd.print("POLLUTION");
lcd.setCursor(0, 1);
lcd.print("DETECTED");
delay(2000) ;
lcd.setCursor(0, 0);
lcd.print(" ");
lcd.setCursor(0, 1);
lcd.print(" ");
lcd.setCursor(0, 0);
lcd.print("Please put in");
lcd.setCursor(0, 1);
lcd.print("filter pack");
swiSta=digitalRead(swi);
while(1==1){
if(swiSta == HIGH){
goto exe;
delay (100);
}
swiSta=digitalRead(swi);
}
exe:
lcd.setCursor(0, 0);
lcd.print(" ");
lcd.setCursor(0, 1);
lcd.print(" ");
lcd.setCursor(0, 0);
lcd.print("Purification");
lcd.setCursor(0, 1);
lcd.print("Starts");
while (1==1){
digitalWrite(7,HIGH) ;
digitalWrite(6,LOW) ;
analogWrite(motp,75);
}
}
else {
digitalWrite(13,LOW);
lcd.print(" ");
lcd.setCursor(0, 1);
lcd.print(" ");
lcd.setCursor(0, 0);
lcd.print("NO POLLUTION");
lcd.setCursor(0, 1);
lcd.print("DETECTED");
while(1==1){
delay(100000);
}
}
}
Wiring and assembly (drawing):
Wiring and assembly (photo):
Design Process
Our first design was as simple as a reaction tank with several boards with stainless steel wires weaved in a crisscross pattern as detectors. Although it might be effective for its purification aspect, it is hard to ensure that bacteria stay on the detection boards. Even if a metal-binding domain is added, there will not be enough bacteria stuck onto it. It is even harder to quantify the fluorescence due to the reflection caused by stainless steel. It is also a problem as detection and purification are going on simultaneously: the concentration changes, making detection less accurate.
Image 6. Computer Rendering of Version 1
Thus we designed our second model: we have separated our detection module from the purification module. The container is split into two, one filled with our detector strain and the other with our bioremediation strain. Indeed, this makes the detection more accurate, and no metal-binding domains are needed. However, it is very difficult to fix the fluorescence detection device onto the chamber, and it is inflexible: if we scale its size up, the detector would become too large to operate.
Image 7. Computer Rendering of Version 2
Therefore, we decided to furtherly modularize the device, and we sought for inspiration from ordinary water filters. This is where we designed the third and final version, as described above in this section.