Introduction: Activated sludge process
Activated sludge process is now a widely used aerobic biological waste water treatment method. It could remove organic pollutants from water, which can be consumed by microorganism. It was invented by Clark and Gage in the UK in 1912.
In the early 20th century, waste water treatment was still a headache for cities, especially for big cities like London. At that time, people happened to discover that some sludge sediment appeared in the stagnant water, and the water above became clear!
In fact, the sludge is a biological floc composed of bacteria and protozoa which feed on the organic pollutants, and could oxidize the carbonaceous and nitrogenous matter in the waste water when oxygen presents.
Nowadays this principal has developed into various mature industrial processes and bio-reactors. And the basic work-flow is shown in Fig 1.
A generalized, schematic diagram of an activated sludge process
Originally uploaded by Mbeychok at here.
We designed and assembled a hardware(shown in Fig. 2&3 and the Hardware Operation Demonstration Video) imitating the biochemical pools in waste water treatment plants (WWTPs) at the ratio of 1:50, including handmade microporous tube aerators and flux control and monitor equipment for air and water, which could be used for the experiments of variable aerobic biological treatment methods in laboratory, and the working capacity tests for new types of engineered microorganism under the real conditions in WWTPs.
On top of the traditional biochemical pool construction, we adopted pitched V-shaped bottom and vertical water inlet, and added partitions with holes in the pool, which could improved the practical performance of the working organism.
Our whole set of device
Micro-porous tube aerators
To ensure effective aeration, the aerator is required to provide small and homogeneous bulbs. So we made holes on steel and PVC pipe, and assemble them together. Thus we made micro-porous tube aerators by hand.(shown in Fig. 4&5)
Micro-porous tube aerator
Holes on the steel and PVC pipe
There are two types of tube aerators: the long ones are placed at the V-shaped grooves, while the short ones are placed at the sludge collecting grooves near the front and behind walls.(shown in Fig. 6&7)
Two types of tube aerators
The placement of aerators
Pitched V-shaped bottom
To make sludge collection and removal more convenient and efficient, we constructed V-shaped and pitched bottoms with a groove to collect the sludge produced in the purifying process.(shown in Fig. 8)
Pitched V-shaped bottom
Vertical water inlet
To realize equivalent water-in, we came up with the vertical water inlet, making from PVC pipe with small holes on both sides.(shown in Fig. 9)
Vertical water inlet
Blueprints of the Bio-pool
Three-view diagram of the bio-pool
Size of the bio-pool
At first, we plan to make the engineered bacteria attach to some substrate materials like plastics. However, the model organism we choose to use, E. coli, cannot express bio-film protein naturally. We tested the attach property of the bacteria using materials provided by Nanjing-China, and the result is negative.
Thus, we chose Activated Sludge Method instead of Contact Oxidation Method which uses plastic substrate with working organism attached in the form of bio-film.
To test whether the engineered bacteria could grow and work in the bio-pool, we prepared 30L 1:10 diluted LB with 15g ≥10%tetracycline hydrochloride(for livestock and poultry raising) and 200mL saturated E. coli, added them into one bio-pool and started aeration as is shown in Fig. 12.
After 40 hours, it could be seen observably that the liquid in the pool became unclear with plenty of bacteria suspended in the water.(shown in Fig. 13)
Test (40h later)
When it come to the simulating waste water used in the experiment, we received the recommendation from Nanjing-China. The standard formula of simulating waste water is as following:
Glucose 0.3 g, tryptone 0.1 g, yeast extract 0.01 g, CH3COONa 0.15 g, NaCl 0.05 g, MgSO4·7H2O 0.236 g, K2HPO4·3H2O 0.147 g, NH4Cl 0.18 g, DI water 1 L, 115℃ 30 min sterilization.
The total phosphorus(TP) of the simulating waste water is 20 mg/L since all of the phosphorus in the water comes from the K2HPO4·3H2O added. By changing the amount of K2HPO4·3H2O, we can adjust the TP in the simulating waste water according to experimental demand.