Lecture 10 (Introduction to wastewater treatment)

Question 1

What is the overall purpose of wastewater treatment?

Answer 1

Removing P, N and organic matter

Question 2

How does wasterwater treatment work in general:

Answer 2

1. Screening and Pumping
   a. The incoming wastewater passes through screening equipment where objects such as rags, wood fragments, plastics, and grease are removed.
2. Grit Removal
   a. In this step, heavy but fine material such as sand and gravel is removed from the wastewater.
3. Primary Settling
   a. The material, which will settle, but at a slower rate than step two, is taken out using large circular tanks called clarifiers. The settled material, called primary sludge, is pumped off the bottom and the wastewater exits the tank from the top. In this step, chemicals are also added to remove phosphorus.
4. Aeration / Activated Sludge
   a. Through biological degradation, the pollutants are consumed by microorganisms and transformed into cell tissue, water, and nitrogen.
5. Secondary Settling
   a. Large circular tanks called secondary clarifiers allow the treated wastewater to separate from the biology from the aeration tanks at this step, yielding an effluent, which is now over 90% treated. The biology (activated sludge) is continuously pumped from the bottom of the clarifiers and returned to the aeration tanks in step four.
6. Filtration
   a. The clarified effluent is polished in this step by filtering through 10 micron polyester media. The material captured on the surface of the disc filters is periodically backwashed and returned to the head of the plant for treatment.
7. Disinfection
   a. To assure the treated wastewater is virtually free of bacteria, ultraviolet disinfection is used after the filtration step. The ultraviolet treatment process kills remaining bacteria to levels within our discharge permit.
8. Oxygen Uptake
   a. The treated water, now in a very stabilized high quality state, is aerated if necessary to bring the dissolved oxygen up to permit level.

Question 3

How do we achieve energy neutrality in wastewater treatment?

Answer 3

• Identify energy optimization opportunities; concentrate on short-term, readily implementable scenarios to reduce consumption and/or increase generation, decreasing GHG emissions.
• Identify and document all options, including longer-term opportunities for positive net energy status for future consideration.
• Plant-wide mass and energy balance model used to evaluate operational and facility energy optimization scenarios.
• Collaborative approach identified “operational” path to energy self-sufficiency
• More advanced technologies.
  o Implementing side stream and mainstream deammonification for N control.
  o Investigate the possibility of using MABR system.
  (MABR = Membrane aerated biofilm reactor, this technology provides a revolutionary improvement in aerobic wastewater treatment due to its highly efficient nutrient removal and its energy efficiency, compared to traditional wastewater treatment systems.)

o Implementing ANAMMOX –> saves energy because we don’t need the aeration tanks (or at least not the full capacity).