Dear Elisabeth,

Thanks a lot for your questions.

Unfortunately, the Master research project remained an exploratory laboratory investigation and we didn’t conduct any techno-economical study. So I cannot answer your question with certitude. Nonetheless, I can assume that microfiltration and ultrafiltration could be a cost-effective solution for urine treatment in the context of a developing country, based on the cost of the equipment that is not excessively high (pump, membrane, etc…). However, fouling of the membranes could be a problem, as demonstrated in the master dissertation, which could lead to high maintenance requirements (need to clean the membranes regularly, long downtime due to maintenance, need to replace the membranes often, etc…). As fouling depends on the flowrate of the liquid to filter, I can imagine microfiltration and ultrafiltration as a suitable solution for urine management in places where there is need to treat low volumes of urine, or in places with enough technical expertise to implement solutions to mitigate fouling (through pre-treatment processes, implementation of technical solutions to avoid fouling during operation or to wash the membranes in a short time).

The reject of microlfiltration / ultrafiltration is mainly composed of particles and micro-organisms, so I can see difficult its direct reuse. In contrast, I believe that the permeate, mainly composed of short organic molecules and salts, could be directly used under certain conditions with low restrictions (e.g.: irrigation for certain crops and certain soils that can stand high salinity) . Nonetheless, I would recommend a further processing to get more refined products. Indeed, I am afraid that some microorganisms (particularly viruses) and micro-pollutants (such as pharmaceutical products) could be still present in the permeate. I admit that the Master thesis is contradictory with respect to the use of the permeate, and I should have been more vigilant during its review.

I hope that my answers were satisfactory.

Kindly,
Santiago

Dear Santiago,

Thanks so much for posting these MEng theses here and also uploading them to the SuSanA library.* I wish more academics would follow suit and do the same thing as a matter of course!

Regarding this particular research, I glanced through the conclusions and perspectives but I was missing some information on costs of this method. Can you imagine it being cost effective in a developing country context? If yes, then in which scenario?

Also could you explain a bit more what was meant with this (page 62):

MF/UF can be used as a pre-treatment step in urine processing for nutrient and water
recovery. The pre-treatment would help reduce the TSS and particle size so as to minimize
fouling in other membrane processes with smaller pore size such as nanofiltration and
reverse osmosis. Micro-pollutants and viruses can be present in the permeate (as indicated
by the COD) Furthermore, valuable salts to agriculture (N, P, K), are also in the permeate
as well also harmful salts ( Na, Cl) Based on these reasons, it is recommended to further
treat the urine instead of directly reusing of the permeate

Did I understand right that the permeate and the reject would both not be directly usable for anything? What could be done with the two streams?

On page 17 of the thesis it was said:

This is because these membranes are economical and efficient in operation thus they could be used as
pre-treatment for further applications (reverse osmosis and nanofiltration) and could also lead to
direct use of the permeate.

This is contradictory to the later finding that direct use of the permeate is not possible?

Elisabeth

* To view all six MEng/MSc theses that Santiago recently uploaded to the library under his partner profile, see here and scroll down a bit below their projects:
www.susana.org/en/community/partners/list/details/148

Title of the thesis: Microfiltration / ultrafiltration of stored urine and urine diluted with water

Date of publication: 2016

Author: Joyce Ouma

Affiliation: Pollution Research Group, University of KwaZulu-Natal

Supervisors: Dr. Santiago Septien Stringel; Dr. Jon Pocock; Pr. Chris Buckley

Abstract: Sanitation is a major challenge for developing countries. According to World Health Organization (WHO) and United Nations International Emergency Children’s Fund (UNICEF), approximately 2.5 billion people in developing countries lack access to proper sanitation facilities (WHO and UNICEF (2013). This has led to the spread of water borne diseases and reduction of the quality of life of the affected people. The “Reinvent the Toilet Challenge” (RTTC) which is an initiative of the Bill & Melinda Gates Foundation aims is to setup novel sanitation systems and find a hygienic and sustainable disposal route for human waste. Membrane technology such as microfiltration/ultrafiltration, nanofiltration, reverse osmosis and forward osmosis can be used for this purpose.
The main objective of this study was to explore the use of microfiltration/Ultrafiltration membranes to determine the parameters that affect the performance of the membranes when filtering two types of urine: stored urine representing the stored feedstock which could be obtained from Urine Diversion Dry Toilets (UDDT); diluted stored urine representing the feedstock which could be obtained from urinals. This was based on the study of flux, permeability, fouling potential and rejection. This study was limited to stored urine which is more stable than fresh urine.
A stirred Amicon® cell in dead-end filtration mode was used in a range of constant transmembrane pressures (TMP) between 10 and 60 kPa. All the membranes used in this study were similar with the same material and molecular weight cut off (MWCO) of 500 kilo Daltons (kDa). Permeability of the membrane before and after filtration, and after cleaning was determined by measuring flux against transmembrane pressure using deionised water. Fouling potential was determined using the modified fouling index (MFI). Physico-chemical characteristics, including particle size distribution analysis, of diluted and undiluted urine before and after filtration were also determined for the purpose of determining membrane rejection. Three cases were studied during these experiments. Case 1 and case 2 involved filtration of undiluted urine while case 3 using diluted urine (at 1:5 ratio of urine to water). For case 1, the experiment was set to start from low to high transmembrane pressure while in the opposite direction for case 2. Case 3 pressure was operated in a similar manner as case 1.
The results indicated that diluted urine had flux significantly higher than undiluted urine with maximum values of 43 and 26 L.m-2.h-1 respectively. Water recovery after a filtration duration of one hour was approximately 40% and 20% for diluted urine and undiluted urine respectively. Permeability of the membranes was lowered significantly, after filtration up to 95%. After cleaning, approximately 80% of permeability was recovered for case 1 and case 3 while approximately 40% was recovered for case 2. Higher membrane resistance due to the cake and irreversible fouling were observed for case 2 (up to 50% higher) compared to case 1 and case 3. It was speculated that particulate matter (larger than 0.1 μm) and colloidal organic matter were the important foulants. According to the modified fouling index, undiluted urine had a higher fouling potential (volume flowrate of 0.089 L.h-1) compared to diluted urine (volume flowrate 0.16 L.h-1). As expected, the specific cake resistance was lower for undiluted urine compared to diluted urine The permeate obtained after urine microfiltration/ultrafiltration was much less loaded in suspended solids compared to the feedstock, but the concentration of the ionic species remained similar.

Keywords: urine; filtration; membrane; flux; fouling; rejection; reuse.