#include <Servo.h>
Servo servodry; // create servo object to control a servo for dry waste container
Servo servowet; // create servo object to control a servo for wet waste container
Servo servomet; // create servo object to control a servo for metal waste container
int val;
int sensor_pin =  ; //pin declaration

void setup() {
  pinMode(led_pin, OUTPUT);
  pinMode(sensor_pin, INPUT);
  servodry.attach(*pin*); // attaches the servodry on pin *pin* to the servo object
  servowet.attach(*pin*); // attaches the servowet on pin *pin* to the servo object
  servomet.attach(*pin*); // attaches the servomet on pin *pin* to the servo object
}

void loop() {

  val = map(val, 0, 1023, 0, 180);
  if(digitalRead(sensor_pin) == HIGH){
    for(val=0; val<=90; val++)//this is to open lid of container of wet waste (i dont know your hardware settings so change according to it) val is in terms of angle
    {
      servowet.write(val);// sets the servo position according to the scaled value
    }
    delay(3000);
    for(  ;val>=0;val--) //this is to close lid of container of wet waste (i dont know your hardware settings so change according to it) val is in terms of angle
    {
       servowet.write(val);// sets the servo position according to the scaled value
    }
  }
  else {
     for(val=0; val<=90; val++) //this is to open lid of container of dry waste (i dont know your hardware settings so change according to it) val is in terms of angle
    {
      servodry.write(val);// sets the servo position according to the scaled value
    }    
     delay(3000);
    for(  ;val>=0;val--) //this is to close lid of container of dry waste (i dont know your hardware settings so change according to it) val is in terms of angle
    {
       servowet.write(val);// sets the servo position according to the scaled value
    }
  }
}