Investigating Nutrient Limitation and Microbial Imbalances in Greywater Treatment

Abstract

Greywater, which comes from household sources such as showers, laundry, and dishwashing, is typically less polluted than toilet wastewater and can be treated and reused. In Helsingborg, Sweden, the RecoLab collects and treats greywater from Oceanhamnen separately as part of a source-separated wastewater system. However, the system has experienced is-sues with filamentous bacteria overgrowth, raising concerns about potential nutrient imbalances that could disrupt microbial processes.
This thesis investigated nutrient dynamics and potential microbial imbalances in greywater treatment at RecoLab. The study focuses on availability of the concentrations of carbon, nitrogen, and phosphorus in influent greywater and evaluates their balance using Total Organic Carbon (TOC) as a measure of biodegradable carbon.
A total of eight days of influent greywater samples were analyzed, with two sets of samples collected per day: one representing fresh greywater taken directly from Oceanhamnen, and the other taken after the greywater had remained in the collection tank for approximately 12 hours. All samples were analyzed for COD, TN, TP, and other key fractions. TOC is a more accurate indicator of bioavailable carbon. A conversion from COD to TOC was employed for a more accurate representation. However, when using TOC in C:N:P ratio, both nitrogen and phosphorus were found to be inadequate relative to carbon in the influent greywater. It became clear that greywater entering the treatment system may contain more bioavailable carbon in relation to nitrogen and phosphorus. Although this does not necessarily cause the overgrowth of filamentous bacteria, such imbalances can affect microbial stability and treatment efficiency. Implementing effective monitoring alongside the dosing of nitrogen and phosphorus into the system could support microbial health and facilitate the proper decomposition of organic matter.

This study provides a foundation for optimizing nutrient management in greywater treatment systems to improve operational stability and effluent quality. It also indicates that careful monitoring of TOC-based nutrient ratios is essential for effective greywater treatment.

Popular Abstract

The science behind smarter water reuse

Greywater isn't as dirty as toilet water but still needs treatment before it can be reused. Every time when we wash our hands, do the laundry, or take a shower, we create this greywater. For treating greywater separately, an advanced treatment facility called RecoLab has been collecting wastewater from Helsingborg's Oceanhamnen area, for the last two years. In this facility, wastewater is collected through three different pipes and treated individually to recover nutrients, gas, and energy.

A recent master's thesis from Lund University examined how effectively RecoLab is managing this task. The study investigated whether the tiny microbes that break down waste in greywater are receiving the proper nutrients to perform their function. These microbes require a balanced diet, particularly the right combination of carbon, nitrogen, and phosphorus. An imbalance in any of these elements can disrupt the system and lead to issues such as excessive bacterial growth.

Over several weeks, samples were collected from the greywater system and tested in the lab. The study found that while the greywater had enough organic material, and it often contained less nitrogen and phosphorus. Or in another way, the greywater had relatively high levels of organic matter but still contained insignificant amounts of nitrogen and phosphorus. When there isn’t enough of nitrogen and phosphorus compared to organic matter, the system can become unbalanced. This may not cause immediate or severe issues, but it could slightly limit microbial activity, especially for high-efficiency treatment systems. In such cases, operators might need to dose nitrogen and phosphorus into the system to maintain microbial health and ensure proper breakdown of organic matter.

This suggests that even the water from washing activities can be managed more intelligently and recycled, preserving drinking water for essential uses. At the same time, it highlights the role of research and development in guiding towards better sustainability and environmental protection. Understanding and managing these nutrient levels can help treatment plants avoid problems, reduce costs, and make better use of recycled water.

• author: Raphel, Aiswarya
• supervisor: Åsa Davidsson
• organization: Chemical Engineering (M.Sc.Eng.)
• course: VVAM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Water Resources Engineering, greywater, Nutrient Limitation
• language: English
• id: 9193287
• date added to LUP: 2025-06-10 09:23:10
• date last changed: 2025-06-10 09:23:10