Photo Activated Sludge

IHE Delft is working with IIT Delhi to pilot a photo activated sludge system to remove nutrients from the drain water of the Barapullah Drain. In Pavitra Ganga it will be tested in combination with cleaning blocks.

Working principles

The fundamental principle governing the operation of the photoactivated sludge (PAS) reactor is to cultivate a mixed consortium of algae and bacteria (e.g. activated sludge/nitrifiers) to removal pollutants of interest from the Barapullah drain. The latter could be heterotrophs, nitrifiers, or, even anammox bacteria. 

PAS technology differs from conventional pond systems in that it optimizes the growth of the mixed consortia (i.e. due to the daily light/dark cycles) and the pollutant removal rates are much higher due to higher biomass concentration and the good mixing characteristics achieved in the PAS.

The domestic sewage flowing in the Barapullah drain poses a threat to the environment due to their high pollutant load, which can lead to eutrophication of water bodies and a decline in the ecosystem quality.

It is expected that the ammonium removal rates will be increased by the nitrifying bacteria, which were supplied with oxygen provided by the algae. The addition of bacteria to the microalgal culture increases the biomass retention capacity, allowing the hydraulic retention time (HRT) and solids retention time (SRT) to be decoupled. 

One of the other advantages of the PAS is the fact that the microalgal-bacterial system provides the potential for a reduction in HRT, thereby reducing the large area requirements typically demanded by algal systems.

The PAS reactor at our demonstration site is a 1500 L capacity raceway pond. The reactor is first being operated in batch mode to cultivate the microalgae and nitrifiers. After acclimation, i.e. when the reactor reaches steady state, the reactor will be operated in photo-sequencing mode, with 1 or 2 cycles per day, and the following parameters will be monitored weekly: BOD, COD, TOC, TIC, TSS, VSS, PO4-P, NH4-N, TN, NO2-N, NO3-N, DO, CO2, pH, temperature, chlorophyll - a, lipid content, and biomass productivity.

Photoactivated sludge


Main research questions

The main research questions of this project can be stated as follows:

  1. What is the maximum nutrient removal efficiency of the PAS system under the prevailing Indian climatic conditions, in terms of g N removed/m2/day, per sunlight input (gN/mol photons), and the energy consumption (g N/kWh)?
  2.  How do different operational parameters (HRT, pond depth, and biomass concentration) influence the efficiency of nutrient removal and biomass production?
  3.  What are the possible resources that can be recovered from the algal biomass and what are their downstream recovery techniques?

More information

For more infomration contact Peter van der Steen, Head of the Water Supply, Sanitation and Environmental Engineering Department, Associate Professor of Environmental Technology, IHE Delft Institute for Water Education, Delft, the Netherlands

Involved partners