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The toxicity and risk of household products to the vermifiltration wastewater treatment process

Hughes, R.J. (2010) The toxicity and risk of household products to the vermifiltration wastewater treatment process. PhD thesis, Murdoch University.

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Abstract

Vermifiltration systems are wastewater treatment systems that rely upon earthworms (worms herein) to produce a self-sustaining vermicompost filter from wastewater solids. The vermicompost filter produced by the worms removes wastewater solids, oxygenates the wastewater, adsorbs many wastewater constituents and improves the quality of the wastewater. Vermifiltration systems have low energy requirements and appropriately performing systems can provide high levels of wastewater treatment with no odour.

The toxicity and risk of household wastewater to vermifiltration systems is a critical area of research because the application of vermifiltration systems is expanding. However, there were no studies found in the literature on how to assess and manage the risk of household wastewater to vermifiltration systems. The assessment and management of wastewater toxicity and risk to vermifiltration systems is important because without an adequate understanding of the risk from household wastewater, the toxicity caused by different household wastewater constituents to the vermifiltration systems, and in particular the worms in the systems, may lead to system failure. Moreover, by understanding the risk that wastewater constituents pose to vermifiltration systems, the risk can be managed through appropriate procedures.

This research was conducted to assess the toxicity and risk of household wastewater to the vermifiltration process and provide suitable management options which reduce the risk of household wastewater toxicity. The study contained four major research phases. In sequential order they were:

1. A household product survey that identified common toxic household product ingredients for toxicity testing;
2. A series of toxicity tests on the toxicity and risk of common toxic ingredients that may accumulate in the vermifiltration process;
3. A series of toxicity tests on the toxicity and risk of common toxic ingredients in the influent of household wastewater to the vermifiltration process; and
4. A series of toxicity tests using the most toxic household products (and ingredients) in full scale systems.

The study concluded by providing management procedures to reduce the risk from toxic household products to vermifiltration systems.

The household product survey was the first phase of the research upon which the other phases relied: The survey firstly identified the ingredients that had the highest occurrence and mass in household products and then identified the most toxic household product ingredients by comparing the toxicity, octanol water partitioning constant and biodegradation rate of the ingredients with a high occurrence and mass. The ingredients identified as the common toxic household ingredients were sodium, hypochlorite, ammonia, sodium hydroxide, linear alkylbenzene sulfonate (LAS), sodium dodecyl sulfate (SDS), and benzalkonium chloride (BAC).

The accumulation toxicity tests examined the toxicity and risk of the common toxic household ingredients from accumulation in a vermifiltration system. The research found that all the ingredients, except BAC, pose a low risk to a vermifiltration system. The research found that the presence of worms enhanced biodegradation of all the surfactants, especially BAC.

The influent toxicity tests examined the toxicity and risk of the common toxic household product ingredients at predicted influent wastewater concentrations. The research found that most of the ingredients and household products would be toxic and would exhibit a high risk at the predicted influent concentrations. However, it was noted in the risk assessment that the volume of wastewater with which the household products would be discharged would change between products, with most being discharged with a low volume of wastewater e.g. 1-5L. Therefore, it was concluded that some products may not actually pose a high risk in a full sized system because the low volume of water with which they would be discharged may cause them to have a low residence in the system, causing a low exposure time. The full scale experiments on household products were conducted to clarify this assumption.

The full scale toxicity tests were conducted to compare the data from the accumulation and influent toxicity risk assessments. The full scale toxicity tests showed similar findings to the influent toxicity experiments for adult worm mortality. The full scale toxicity tests did however find that the worms would move away from the areas most affected by toxic household products and recolonise those areas after the ingredients in the products had moved through the· system. The migration of the worms reduced the risks of reproduction toxicity, as the movement of worms away from sub lethal toxicity stress would enhance the reproductive potential of the worms. Due to this, it was proposed that the system under study, which discharged the influent unevenly in the top bed of the vermifiltration system, would be best assessed using adult mortality as the main endpoint. However, it was also proposed that systems with an even discharge of influent should still be assessed using reproduction, as the worms in these systems would be unable to migrate away from the ingredients.

The risk assessments and full scale toxicity tests led to the development of management procedures for the most common household products. It was proposed that household products used at the recommended dose would pose a low risk to vermifiltration systems, as identified in the full scale research. It was also proposed that where a product is used above the recommended dose a site specific (system specific) risk assessment is undertaken.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: A digital copy of this thesis is not available. Your library can request a copy from Murdoch University Library via Document Delivery. A fee applies to this service.
Supervisor: Nair, Jaya, Ho, Goen and Mathew, Kuruvilla
URI: http://researchrepository.murdoch.edu.au/id/eprint/37806
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