Blackwater

Question 1

How was wastewater historically managed?

Answer 1

o Dumping on the street
 Diseases, contaminated groundwater and drinking water
o Dry toilets
o Pipe network
 Direct into waterbodies

Question 2

Describe the development of conventional WWTP

Answer 2

o 1930 – mechanical treatment
 Stops particles.
 Sedimentation in tanks
o 1950 – biological treatment
 Bacteria decompose nutrients and pathogens
 Ex: biological reactor
* Influent -> microorganism degradation -> aerated zone -> secondary clarifier -> settling of organic material -> effluent & return of sludge
o 1970 – chemical treatment
 Adding substances for treatment.
 Flocking flotation etc
o Next: micropollutants

Question 3

Describe the composition of C, N and P for yellowwater and brownwater

Answer 3

o Yellowwater
 C 12%
 N 87%
 P 54%
o Brownwater
 C 47%
 N 10%
 P 47%

Question 4

What does blackwater consist of?

Answer 4

Faeces, urine, toiletpaper, flushwater, pathogens, pollutants, micropollutants

Question 5

Mention simple ways blackwater can be treated and how nutrients can be extracted

Answer 5

• Wet composting
  o In rural areas
• Dry composting
  o Simple
  o Eco friendly
  o Long composting time
  o Urine can be separated
• Anaerobic treatment
  o Degrades organic matter to methane
• Struvite extraction
  o Phosphorus recovery
• Ammonia stripper
  o Nitrogen recovery

Question 6

How does temperature affect anaerobic treatment?

Answer 6

o Higher temperature – more pathogens reduced. Takes more energy to heat the blackwater.
o Lower temperature – longer time needed

If the operating temperature is low, a high SRT is required for sufficient
anaerobic degradation. Under such conditions, reactors with enhanced biomass
retention should be chosen. Otherwise, the required reactor volume will be very large. Besides their large volume, low temperature reactors have further
disadvantages.MoreCH4, a potent greenhouse gas, will leave the anaerobic
reactor dissolved in the effluent andwill later escape to the atmosphere. In
contrast, high temperatures, that is thermophilic treatment, increase pathogen reduction and extend the possibilities of safe sludge reuse.

Question 7

Describe the process of anaerobic treatment

Answer 7

 Hydrolysis – breaking of the water molecule
* Large polymers -> small
 Acidogenic bacteria convert organic compounds -> volatile fatty acids and CO2
 Acetogenic bacteria convert VFA -> H2 and CO2
 Methanogenic bacteria + acetic acid or H2 and CO2 -> CH4

Question 8

Describe two anaerobic treatments with same biomass retention

Answer 8

 Continuous stirred-tank recovery (CSTR reactor)
* For highly concentrated waste – blackwater from e.g. vacuum toilets
* Fed continuously
* Liquid and suspended solids, including biomass, are completely mixed
* The concentration and composition of the reactor content is equal to that of the effluent
 AC reactor
* Accumulation – digestion and storage in one volume
* Inflow but no outflow, a reactor that fills up, treats the wastewater and is then emptied.

Question 9

What is an anaerobic treatment with enhanced biomass retention?

Answer 9

 Upflow anaerobic sludge blanket (UASB)
* Blanket of anaerobic bacteria breaking down organic matter to biogas and biomass
* Suspended solids help retain the sludge in the reactor
* Enters at bottom - passes upward through a dense anaerobic sludge bed – organic substances in the wastewater reacts with the sludge – the soluble substances are converted to biogas and the suspended ones are entrapped in the sludge where they start degrading. Granules/ flocs are produced as the water and gas moves upward. If the wastewater is rich in suspended solids (such as blackwater), bigger flocculents are formed instead- which does not settle as well. Longer time is needed if the wastewater is rich in many suspended solids.

Question 10

What is the difference between the two kinds of reactors for anaerobic treatment?

Answer 10

In the first approach, the waste stream and the active biomass have the
same retention time in the reactor, that is the hydraulic retention time (HRT) and
the sludge retention time (SRT) are equal. The second type of reactors allows a
long retention of the biomass, so that the SRT significantly exceeds the HRT.
The second system is advised for anaerobic treatment of wastewaters, while
systems without biomass retention are more appropriate for slurries or solid wastes

Question 11

What determines the size of the anaerobic reactor system?

Answer 11

The slowest conversion process will determine its size. In
general, hydrolysis is the rate-limiting step in the anaerobic conversion of
complex substrates, which usually have a high fraction of suspended organics,
consisting of lipids, carbohydrates and proteins. The hydrolysis rate will therefore
determine the size of the anaerobic reactor system.

Question 12

How are pharmaceuticals and hormones treated with anaerobic methods`?

Answer 12

Insufficiently