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Quality Assessment of sludge from Glen Valley WWTP and its potential as fertilizer

Åberg, Ellen LU and Norup, Johanna LU (2015) VVA820 20151
Chemical Engineering
Abstract
The use of sludge as fertilizers contributes to the recycling of nutrients to the environment due to its origin from wastewater and therefore relatively high content of nutrients and organic matter. However, wastewater does also contain hazardous compounds like heavy metals and micropollutants which eventually are separated to the sludge during the treatment processes at the wastewater treatment plant. In order to improve the sludge quality, source tracking is a relatively cheap and effective way to find and eliminate hazardous compounds and prevent them from ending up in the sludge.

The aim with this thesis was to investigate the fertilizer potential in sludge from Glen Valley wastewater treatment plant (GWWTP) in Gaborone, Botswana.... (More)
The use of sludge as fertilizers contributes to the recycling of nutrients to the environment due to its origin from wastewater and therefore relatively high content of nutrients and organic matter. However, wastewater does also contain hazardous compounds like heavy metals and micropollutants which eventually are separated to the sludge during the treatment processes at the wastewater treatment plant. In order to improve the sludge quality, source tracking is a relatively cheap and effective way to find and eliminate hazardous compounds and prevent them from ending up in the sludge.

The aim with this thesis was to investigate the fertilizer potential in sludge from Glen Valley wastewater treatment plant (GWWTP) in Gaborone, Botswana. The sludge is analyzed in terms of nutrient and heavy metal contents as well as physiochemical parameters. In order to determine the potential as fertilizer, the quality of the sludge is compared with other fertilizer alternatives, other sludge types and regulations for sludge use in agriculture. The work with sludge quality improvements in Gaborone is also investigated. Sludge from different stages along the treatment processes were collected in order to see differences in quality related to the treatment.
The results shows that the samples of primary anaerobically treated sludge tend to have higher heavy metal content than the secondary sludge. The quality of the dry sludge samples indicates lower nutrient content than both the primary and secondary sludge, but similar heavy metal content. The analysis of dry sludge from GWWTP indicates a low nutrient value and high heavy metal content in comparison to other selected fertilizer options and sludge from other WWTPs. The processes for removal of nutrients from the wastewater are an important factor for the nutrient content in the sludge.

The sludge from GWWTP is currently sold as fertilizer and soil conditioner. In order to get a sustainable sludge production and a safe fertilizer alternative, a clearer strategy for the management and analysis of the sludge could be established. There is no found legislation of sludge quality for agricultural use in Botswana but it was found that arsenic, copper, lead and zinc exceeded the limits according to the South African regulations that are likely to be implemented in Botswana in the future. The Swedish limits were exceeded for lead and zinc.

The work with source tracking in Botswana is conducted in the Trade Effluent Agreement (TEA) where the strategy is to make an agreement with industries to only discharge wastewater to the sewer system that is approved by the country’s water authority. There is a challenge in getting industries to participate in the agreement.

The result from this thesis is only based on one single sampling occasion. A continuous and more frequent sludge quality analysis work must be done in order to determine the actual potential as fertilizer. The result presented in this report does though indicate that the quality of the sludge needs to be improved before it can be assured that the sludge is safe and sustainable to use as fertilizer for food production. (Less)
Popular Abstract
As the world’s population increases, the need for fertilizers is also increases. However there is also a demand of finding sustainable fertilizers that does not deplete the natural resources. A possible alternative meeting these criteria is sewage sludge, a cheap and nutrient-rich by-product from the treatment of wastewater. However, the content of hazardous compounds in the sludge must be within acceptable limits in order to meet the requirements for fertilization.

Sewage sludge reflects the society, meaning that it can contain organic matter, nutrients, but also hazardous contents like heavy metals and micropollutants. Organic matter and nutrients are important components for plant growth and therefore a demand for a fertilizer... (More)
As the world’s population increases, the need for fertilizers is also increases. However there is also a demand of finding sustainable fertilizers that does not deplete the natural resources. A possible alternative meeting these criteria is sewage sludge, a cheap and nutrient-rich by-product from the treatment of wastewater. However, the content of hazardous compounds in the sludge must be within acceptable limits in order to meet the requirements for fertilization.

Sewage sludge reflects the society, meaning that it can contain organic matter, nutrients, but also hazardous contents like heavy metals and micropollutants. Organic matter and nutrients are important components for plant growth and therefore a demand for a fertilizer product.
Heavy metals on the other hand can in too high concentrations be harmful both for human health and the environment. Studies have also shown that heavy metals contained in fertilizers (both conventional and sewage sludge) that are spread on agricultural fields tend to accumulate in plants and further to animals and humans.

To eliminate the hazardous compounds in sewage sludge, source tracking can be used – A method to track and reduce hazardous compounds at the source. This is thus a way to prevent that hazardous compounds are even discharged to the sewer network.

Glen Valley Wastewater Treatment plant, GWWTP, receives wastewater from Gaborone city and surrounding areas. The incoming wastewater to the plant originates both from households and industries.

This master thesis investigates the fertilizer potential in sludge from GWWTP and to suggest possible improvements to increase the quality.
Sludge is sampled from five different stages along the plant and the result shows that the fertilizer potential differs for the different sludge sampled. The results was only based on one sampling occasion, which was not enough to determine the fertilizer potential, but there is however indications of too high heavy metal contents and improvements must be made in order to higher the sludge quality. (Less)
Please use this url to cite or link to this publication:
author
Åberg, Ellen LU and Norup, Johanna LU
supervisor
organization
course
VVA820 20151
year
type
H2 - Master's Degree (Two Years)
subject
report number
2015-10
language
English
id
7456043
date added to LUP
2015-08-14 14:06:54
date last changed
2015-08-14 14:06:54
@misc{7456043,
  abstract     = {The use of sludge as fertilizers contributes to the recycling of nutrients to the environment due to its origin from wastewater and therefore relatively high content of nutrients and organic matter. However, wastewater does also contain hazardous compounds like heavy metals and micropollutants which eventually are separated to the sludge during the treatment processes at the wastewater treatment plant. In order to improve the sludge quality, source tracking is a relatively cheap and effective way to find and eliminate hazardous compounds and prevent them from ending up in the sludge.

The aim with this thesis was to investigate the fertilizer potential in sludge from Glen Valley wastewater treatment plant (GWWTP) in Gaborone, Botswana. The sludge is analyzed in terms of nutrient and heavy metal contents as well as physiochemical parameters. In order to determine the potential as fertilizer, the quality of the sludge is compared with other fertilizer alternatives, other sludge types and regulations for sludge use in agriculture. The work with sludge quality improvements in Gaborone is also investigated. Sludge from different stages along the treatment processes were collected in order to see differences in quality related to the treatment.
The results shows that the samples of primary anaerobically treated sludge tend to have higher heavy metal content than the secondary sludge. The quality of the dry sludge samples indicates lower nutrient content than both the primary and secondary sludge, but similar heavy metal content. The analysis of dry sludge from GWWTP indicates a low nutrient value and high heavy metal content in comparison to other selected fertilizer options and sludge from other WWTPs. The processes for removal of nutrients from the wastewater are an important factor for the nutrient content in the sludge. 

The sludge from GWWTP is currently sold as fertilizer and soil conditioner. In order to get a sustainable sludge production and a safe fertilizer alternative, a clearer strategy for the management and analysis of the sludge could be established. There is no found legislation of sludge quality for agricultural use in Botswana but it was found that arsenic, copper, lead and zinc exceeded the limits according to the South African regulations that are likely to be implemented in Botswana in the future. The Swedish limits were exceeded for lead and zinc.

The work with source tracking in Botswana is conducted in the Trade Effluent Agreement (TEA) where the strategy is to make an agreement with industries to only discharge wastewater to the sewer system that is approved by the country’s water authority. There is a challenge in getting industries to participate in the agreement.

The result from this thesis is only based on one single sampling occasion. A continuous and more frequent sludge quality analysis work must be done in order to determine the actual potential as fertilizer. The result presented in this report does though indicate that the quality of the sludge needs to be improved before it can be assured that the sludge is safe and sustainable to use as fertilizer for food production.},
  author       = {Åberg, Ellen and Norup, Johanna},
  language     = {eng},
  note         = {Student Paper},
  title        = {Quality Assessment of sludge from Glen Valley WWTP and its potential as fertilizer},
  year         = {2015},
}