Descriptive Assessment and Amendment of the SimpleTreat Model - Modelling of Organic Chemicals in Sludge for Soil Applications

Abstract

Large quantities and numbers of organic compounds (OCs) from industries and domestic
sources enter the wastewater treatment plants (WWTPs) everyday, which is an ever-increasing
issue in modern society. In WWTPs, the pollutants are either degraded or emitted to the air, the
effluent (water) or the sludge (biosolids). Even though the sludge may contain toxic contaminants
and heavy metals, there is an incentive of recycling sewage sludge as a fertiliser to preserve the
phosphorus that is a limiting resource. To ensure the quality of the sludge, the WWTPs can
certify their work according to the Swedish certification system, REVAQ that includes setting up
an upstream action plan (uppströmsarbete in Swedish) by which to improve the sludge.
Nevertheless, the overall environmental risk of OCs, i.e. from entering the WWTP to exposing
the sludge containing OCs to soil processes, has so far not been taken into consideration in the
upstream action.
This master’s thesis is carried out at SWECO Environment AB in association with the umbrella
project “Organic compounds in sludge recycling, evaluation and prioritisation” for the Swedish
Water & Wastewater Association, in cooperation with four Swedish wastewater treatment plants:
Ellinge, Käppala, Ryaverket and Sjölunda.
The main objective of the thesis is to develop a methodology to predict the fate of organic
chemical pollutants in sludge after being exposed to soil processes by applying and amending the
easy accessible modelling tool SimpleTreat 3.1. However, further investigation of how the soil
processes will affect the removal of the OCs in soil will not be assessed in this thesis. The
SimpleTreat will as well be adapted to existing known parameters of generic Swedish WWTPs
that have not been included in the original SimpleTreat. In addition, the applicability of the
modified model for four generic Swedish WWTP configurations will be validated by comparing
the predicted results of effluent and sludge with measurements from the IVL-database (Swedish
Environmental Research Institute). Furthermore, by simulating measured chemicals in the
influent, a chemical list with expected concentration ranges in Swedish effluent and sludge can be
obtained, especially when many of the emerging chemicals’ presence, frequency of occurrence or
source may be unknown. Since two input parameters from Ellinge are missing, this WWTP has
consequently been left out of the investigation. The old and new sections of Käppala have
different plant configurations and are therefore treated as two separate plants.
In summary, a stepwise methodology presented to predict the distribution of OCs to water and
sludge, which comprises of a plant description, chemical data collection, calibration and
validation. The OCs that are investigated and measured in WWTPs are mostly hydrophobic and
their emissions to air are thus negligible. Moreover, the SimpleTreat model was modified and
proved to be applicable for predicting the fate of organic pollutants with regard to a number of
factors: 1) the model structure, 2) the model parameters and 3) the data quality. Firstly, the
structure of the modified SimpleTreat is limited to a primary settler, an activated sludge system
(anaerobic, anoxic and aerobic zones) and a secondary clarifier. Secondly, the physico-chemical
parameters are preferably experimentally measured but estimated values from EPI (Estimation
Programs Interface) Suite™ are equally satisfactory. Thirdly, the data of influent, effluent and
sludge has to be measured at the right location within a reasonable time frame and employing the
same sampling and analysis method. To improve the results for a specific compound, it is
suggested to measure the partition coefficient Kp in raw sewage, primary settler, aeration tank and
secondary clarifier to gain a more precise prediction of the partitioning in the defined WWTP.
In conclusion, a total of 84 chemicals were modelled in the modified SimpleTreat with the four
plant configurations respectively; the chosen WWTPs attested representative overall pollution
removal rates via effluent and sludge when compared with typical concentrations ranges of the
IVL-database. Predictions of the concentrations’ order of magnitude in Swedish effluent using
the modified SimpleTreat proved to have 92% accuracy and in Swedish sludge 56% accuracy.
However, further analysis of the chemicals must be carried out to classify the risk of the chemical
in soil amendment. Finally, the information that can be acquired by applying all steps in the
methodology is which substances that do not pose a threat to the environment and human health
despite being recycled with sludge, supposing that the concentration level of toxicity is known.

• author: Chieng, Belinda
• supervisor: Xavier Flores; Ulf Jeppsson
• organization: Industrial Electrical Engineering and Automation
• course: EIE920 20122
• year: 2012
• type: H3 - Professional qualifications (4 Years - )
• subject: Technology and Engineering
• keywords: SimpleTreat, organic compounds, REVAQ, soil amendment, methodology, WWTP, fugacity and steady-state model
• publication/series: CODEN:LUTEDX/TEIE
• report number: 5302
• language: English
• id: 3706220
• date added to LUP: 2013-05-20 15:24:35
• date last changed: 2014-09-04 08:29:55