Assessing the Impact of Nitrogen and Phosphorus Addition on Specific Oxygen Uptake Rate in Greywater Treatment

Abstract

Water scarcity is an increasing global challenge, driven by growing population, economic development, agriculture, and climate variability. Reusing greywater offers a sustainable alternative water source for non-potable applications, reducing the demand for freshwater. Proper treatment is essential to ensure safety and prevent environmental pollution. Biological treatment, utilizing microorganisms like bacteria, fungi and algae, is a common method for breaking down contaminants in wastewater. The efficiency of these microorganisms is influenced by factors including nutrient availability.
This study investigates the effect of nutrient additions on the Specific Oxygen Uptake Rate (SOUR) of greywater sludge. Currently, RecoLab a source separated wastewater treatment facility has experienced challenges with filamentous bacterial overgrowth in the greywater treatment line. This problem is suspected to be linked to nutrient limitations. To investigate this, need to determine whether nutrient amendments influence microbial respiration in grey-water sludge and identify which nutrient addition has the most significant impact to the treat-ment process.
A series of laboratory experiments based on the modified SOUR method were conducted on greywater sludge samples collected over seven weeks from RecoLab. The improved experi-mental design included four nutrient additions conditions: a control with no nutrient addition, nitrogen addition, phosphorus addition and a combined nitrogen and phosphorus addition. Specific oxygen uptake rate measurements, normalized by total suspended solids, were rec-orded to evaluate microbial respiration.
The findings obtained from specific oxygen uptake rate experiment indicate that phosphorus addition consistently enhanced the microbial respiration rate, whereas nitrogen addition and the combination of both nitrogen and phosphorus addition did not lead to further improvement beyond that achieved by phosphorus alone. Also, nutrient concentration analysis, which was done by ion chromatography supported this conclusion, showing substantial phosphate uptake when phosphorus was available. This suggests that greywater is nutrient limited, and phospho-rus might be the primary limiting nutrient in the greywater sludge.
However, statistical analysis done by paired t-tests on maximum specific respiration rates showed no significant effect of nutrient additions on microbial respiration rates. Although trends suggest a phosphorus limitation, the absence of statistical significance may be attributable to the small sample size and inherent experimental variability.

Popular Abstract

Feeding the Bugs: Unlocking the Secret to Cleaner Greywater?
Water is essential for life, but only a small fraction of the Earth's water is accessible freshwater. With growing populations and increased water use, many areas face water scarcity. One way to handle this scenario is by reusing greywater, which refers to untreated household wastewater from sources like showers, sinks, and laundry, excluding toilet waste. Greywater makes up a large portion of domestic wastewater, around 40–90%. If properly treated, it can be reused for non-drinking purposes like garden irrigation or toilet flushing, reducing the demand on freshwater supplies. Greywater reuse is presented as a sustainable alternative water source.
Ensuring proper wastewater treatment, including greywater is crucial to protect aquatic eco-systems, safeguard the environment and preserve human health. Untreated wastewater can cause pollution and health problems.
This study seeks to determine how adding nitrogen and phosphorus can improve microbial activity in greywater sludge, with a focus on the challenges observed at the RecoLab wastewater treatment facility in Helsingborg, Sweden. The facility is experiencing treatment challenges with filamentous bacteria overgrowth in the greywater treatment process, which compromises the quality of the effluent water. This overgrowth is linked to a lack of biologi-cally available nutrients.
One effective and simple wastewater treatment method is biological treatment, which relies on microorganisms (Bugs) to break down waste. For the microbes to grow, reproduce and efficiently remove contaminants from wastewater, they require essential nutrients mainly nitrogen and phosphorus. Think of them as needing a balanced diet to do their job well. Thus, feeding these microorganisms with the right ratio of nutrients will support their growth, helps maintain consistent treatment performance, improves effluent quality, and prevents operational issues such as poor sludge settling.
Without an adequate supply of these crucial nutrients, microorganisms may develop deficiencies that compromise their metabolic processes. This can lead to problems in the treatment process like poor treatment efficiency and the unwanted growth of filamentous bacteria, which may disrupt the ability of the sludge to settle. To investigate if nutrient limitation was indeed affecting the microorganisms in the greywater sludge at RecoLab, a study was conducted to measures how quickly these microorganisms in the greywater sludge use oxygen to break down organic matter. A higher respiration rate under nutrients addition indicates more active microorganisms. Thus, nitrogen and phosphorus were added to examine their impact on microbial respiration rates and identify which nutrient acts as the primary limiting factor in microbial activity.
The study shows that phosphorus availability appears to be critical for boosting microbial activity in this greywater treatment process. Thus, feeding the "bugs" the right nutrients, especially phosphorus, might potentially help to clean greywater and prevent any further operational issues to the greywater treatment plant.

• author: Haule, Gratius Francis
• supervisor: Åsa Davidsson; Ashley Hall
• organization: Chemical Engineering (M.Sc.Eng.)
• course: VVAM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Water Engineering, Nitrogen and Phosphorus Limitation, Specific Oxygen Uptake Rate, SOUR, Greywater Treatment
• language: English
• id: 9193773
• date added to LUP: 2025-06-12 08:48:04
• date last changed: 2025-06-12 08:48:04