Kategoriarkiv: Thesis Defense

Licentiate Seminar: Luis Fernando Perez Mercado

Luis Fernando Perez Mercado, Doctoral Candidate at the Environmental Engineering Unit, Department of Energy and Technology will defend his licentiate thesis entitled, On-farm filtration technology for pathogen reduction: Reuse of low hygienic quality water for vegetable irrigation.

When?: 24 October 2017 at 13:30
Where?: Lecture Room 2034, MVM house, Swedish University of Agricultural Sciences

For further information, get in touch with Luis at the Department of Energy and Technology, P.O. Box 7032, SE-750 07 Uppsala, Sweden. E-mail: fernando.perez@slu.se

Abstract:  Reusing wastewater for irrigation has been widely recognized as an effective way to recirculate plant nutrients and water, particularly in arid and semi-arid regions. However, wastewater reuse in agriculture poses several hazards for human health, because of potential introduction of pathogens into agricultural production systems and therefore increasing the disease burden. Risks are higher in developing countries, where conventional wastewater treatment plants face several challenges in adequately treating the wastewater, if at all. In order to feasibly address such risks, a new management approach has been posed in which alternative measures act as barriers along the farm-to-fork pathway. The concept is that a cumulative effect of these barriers reduces exposure to pathogens. The overall aim of this study was to evaluate the hygienic quality of produce from agricultural systems using irrigation water contaminated with wastewater and to assess suitability of an on-farm filtering in this system.

To achieve this objective, the concentration of bacteriophages, E. coli and helminth eggs was measured in lettuce, water and soil during one cropping season in an agricultural system. This agricultural system used wastewater as well as riverbank filtration for irrigation of vegetables in Cochabamba, Bolivia. Five riverbank wells and the associated river were sampled every two weeks during the monitored cropping season. Soil samples were taken from the five plots that were irrigated with the monitored wells when the lettuce was planted and again when harvested. Composite lettuce samples were taken when harvested. In the laboratory, the reduction of bacteriophages (ɸX174 and MS2), E. coli, Enterococcus spp. and Saccharomyces cerevisiae by charcoal filters was investigated in relation to three grain diameter of filtering media. The tested parameters and levels were: two hydraulic loading rates 200 and 400 L m-2 d-1, three grain diameters of the biochar (Ø = 1.4, 2.8 and 5 mm), and two inflowing levels of electric conductivities of 500 and 1000 µS cm-1.

The microbial concentrations found in soil, lettuce and water sources of agricultural system evidenced high probabilities of fecal contamination along the system. Two types of riverbank filtration wells were identified: protected and unprotected. Both types exhibited significant levels (circa 4 log10 E. coli, 2 log10 bacteriophages, 1 log10 protozoa cysts and 70 % helminth eggs) of microbial reduction. Protected wells had significantly higher reduction rates for all microorganisms except virus. Results from biochar filters showed 1 log10 unit removal of all the monitored microorganisms, however, only for the smallest grain diameter (1.4 mm). No difference was found in microbial removal with either tested hydraulic loading rates nor with the tested electric conductivities. Grain diameter and uniformity of filtering media were identified as main factors for microbial removal for the two tested filtration technologies. Full-scale implementation of both is considered extremely context-dependent due to need of specific geological characteristics for riverbank filtration and due to large area requirement for biochar filters.

Posted by Prithvi Simha

Licentiate Seminar: Jenna Senecal

Jenna Senecal, Doctoral Candidate at the Environmental Engineering Unit, Department of Energy and Technology will defend her licentiate thesis entitled, Urea stabilisation and dehydration for urine-diverting toilets: System and hygiene evaluation.

When?: 24 October 2017 at 09:00
Where?: Lecture Room S, Ulls hus, Swedish University of Agricultural Sciences, Uppsala

For further information, get in touch with Jenna Senecal at the Department of Energy and Technology, P.O. Box 7032, SE-750 07 Uppsala, Sweden. E-mail: jenna.senecal@slu.se

Abstract: Over four billion people are discharging untreated human excreta into the environment without any prior treatment, causing eutrophication and spreading disease. This eutrophication is caused by nutrients found predominantly in urine. If managed adequately, urine can be used as a fertiliser because it contains the same plant nutrients as the fertilisers used to produce the food that people eat. Currently to replace the nutrients removed from fields during harvesting, more fertilisers are being manufactured and applied and ultimately more are being leached into the environment.

The use of human urine as a fertiliser is limited by its low nutrient concentration compared with commercial fertilisers. This study sought to increase the nitrogen (N) concentration (from 0.6 % to >6 %) through dehydration to produce a dry fertiliser of monetary value and where no liquid disposal from the toilet is required. The objective of this thesis was to evaluate a treatment that could stabilise urea and concentrate the urine while retaining >80 % of the NKP. Fresh human urine was added at various intervals to wood ash or biochar to first alkalise and thus inhibit the enzyme urease which catalyses the hydrolysis of urea. The urine was then dehydrated at temperatures of between 35 and 65 °C. A hygiene assessment was undertaken to observe the inactivation of five microorganisms (three indicators: Enterococcus faecalis, MS2 bacteriophage and ΦX 174 bacteriophage; and two pathogens: Ascaris suum and Salmonella enterica sub enterica Typhimurium) at the end of the alkaline dehydration process.

Urine mass was reduced by 95 % during dehydration, while preserving up to 90 % of the N and all the P and K. Ascaris inactivation data was fitted to a non-linear regression model, which estimated that 325 days of storage would be required for a 3 log10 reduction at 20 °C and 9.2 days of storage at 42 °C. The bacteria and bacteriophages were below the detection limit within four days at 20 °C. Just collecting urine separately from faeces provides a 5.2 log10 reduction. The material is concentrated during dehydration which results in a 3.5 log10 reduction overall just from urine-diversion.

This alkaline dehydration system installed in new or already existing toilets would greatly simplify the logistics and costs of storing, transporting and applying urine as a fertiliser. The truly innovative feature is the final product, a dry powder with 7.8 % N, 2.5 % P and 10.9 % K on dry weight, i.e. equivalent to commercial fertilisers. After just four days of storage, the dehydrated medium would meet WHO and USEPA guidelines for unrestricted fertiliser use.

Posted by Prithvi Simha