this is the circuit of tds sensor module. i want to know the purpose of highlighted part. before this part,there is full wave percision rectifer. i want to know whether this highlighted part act as filter or what, what is its effect on output..

 

i want to know whether this highlighted part act as filter or what

It's a 2-pole, passive, low-pass filter.
It's used to give a smoothed DC output from the full-wave rectified signal (LTspice simulation below with a simulated 100Hz full-wave rectified input).