title: Environmental Impacts of Effluent Containing EDTA from Dairy Processing Plants

authors: Xie, Congmin Zoe

subjects: EDTA

abstract: Ethylenediaminetetraacetic acid (EDTA) is a well-known chelating agent, and has numerous applications in industries, for example in dairy industry to improve the cleaning efficiency of plant and equipment.

As EDTA is water-soluble and not volatile, it is eventually released into the environment with wastewater effluent. In general, EDTA has a low toxic impact for both humans and natural environments. There are some concerns, however, about its poor biodegradation in conventional wastewater treatment plants and natural environments, and its effect in mobilizing heavy metals from solid phases to pose a risk to groundwater.

In the late 1980's the environmental impact of EDTA was scrutinized in Europe. Since then, treatment and discharge of wastewater containing EDTA is increasingly required as environmental regulations become more stringent. This is the first investigation into the effects of EDTA in New Zealand.

In the New Zealand dairy industry, EDTA has been used as an additive alongside caustic agents to improve cleaning efficiency within dairy processing plants and to minimize dairy wastewater discharge into the environment. There are two main disposal methods of dairy wastes; direct discharge into the local stream after treatment, and spray irrigation onto pasture land. The primary aim of this research is to identify whether EDTA is detectable in the environment after the release of dairy wastes containing EDTA into that environment.

For the first time in New Zealand, an analytical method using reversed-phase ion-pair liquid chromatography, was established to determine EDTA present in dairy wastewater, and then applied to surface water, soils and groundwater with appropriate modifications. Method detection limits were 5  g/L for dairy wastewater, 1  g/L for surface water, 0.15 mg/kg (dry weight) for soils, and 2  g/L for groundwater.

Significant concentrations of EDTA, as high as 83 mg/L, were observed in wastewater from dairy processing plants, when EDTA had been used alongside alkaline cleaning agents. The analyses have shown that approximate 93 % of EDTA was removed in the existing biological treatment process, which is an extended aeration activated sludge process, operated under alkaline pH 8.0-8.2 with a 3-week sludge retention time.

For surface water receiving the dairy effluent, 1 - 2.7  g/L of EDTA were found, and no particular concerns were suggested about the associated heavy metals. 

A quasi one-dimension vertical mixing model and a two-dimension (depth-averaged) 3DD hydrodynamic model were applied to simulate EDTA dispersion in the river. The modelling results for 'a worst case scenario' of high EDTA release combined with a low river flow, suggest that the dairy effluent discharge at the Fonterra Waitoa dairy site will not lead to a significant effect on the Waitoa River in terms of EDTA concentration. 

Investigation of EDTA and heavy metal concentrations in pastoral topsoil and groundwater following the land application of dairy biomass concludes that there are no specific concerns. In contrast, the analyses suggest that heavy metals may be built up over long periods of irrigation with dairy effluent in soils, and then transported to the groundwater in the presence of EDTA. However, more research would be required to clarify this matter.

text: Environmental Impacts of Effluent Containing EDTA from Dairy Processing Plants Ethylenediaminetetraacetic acid (EDTA) is a well-known chelating agent, and has numerous applications in industries, for example in dairy industry to improve the cleaning efficiency of plant and equipment.

As EDTA is water-soluble and not volatile, it is eventually released into the environment with wastewater effluent. In general, EDTA has a low toxic impact for both humans and natural environments. There are some concerns, however, about its poor biodegradation in conventional wastewater treatment plants and natural environments, and its effect in mobilizing heavy metals from solid phases to pose a risk to groundwater.

In the late 1980's the environmental impact of EDTA was scrutinized in Europe. Since then, treatment and discharge of wastewater containing EDTA is increasingly required as environmental regulations become more stringent. This is the first investigation into the effects of EDTA in New Zealand.

In the New Zealand dairy industry, EDTA has been used as an additive alongside caustic agents to improve cleaning efficiency within dairy processing plants and to minimize dairy wastewater discharge into the environment. There are two main disposal methods of dairy wastes; direct discharge into the local stream after treatment, and spray irrigation onto pasture land. The primary aim of this research is to identify whether EDTA is detectable in the environment after the release of dairy wastes containing EDTA into that environment.

For the first time in New Zealand, an analytical method using reversed-phase ion-pair liquid chromatography, was established to determine EDTA present in dairy wastewater, and then applied to surface water, soils and groundwater with appropriate modifications. Method detection limits were 5  g/L for dairy wastewater, 1  g/L for surface water, 0.15 mg/kg (dry weight) for soils, and 2  g/L for groundwater.

Significant concentrations of EDTA, as high as 83 mg/L, were observed in wastewater from dairy processing plants, when EDTA had been used alongside alkaline cleaning agents. The analyses have shown that approximate 93 % of EDTA was removed in the existing biological treatment process, which is an extended aeration activated sludge process, operated under alkaline pH 8.0-8.2 with a 3-week sludge retention time.

For surface water receiving the dairy effluent, 1 - 2.7  g/L of EDTA were found, and no particular concerns were suggested about the associated heavy metals. 

A quasi one-dimension vertical mixing model and a two-dimension (depth-averaged) 3DD hydrodynamic model were applied to simulate EDTA dispersion in the river. The modelling results for 'a worst case scenario' of high EDTA release combined with a low river flow, suggest that the dairy effluent discharge at the Fonterra Waitoa dairy site will not lead to a significant effect on the Waitoa River in terms of EDTA concentration. 

Investigation of EDTA and heavy metal concentrations in pastoral topsoil and groundwater following the land application of dairy biomass concludes that there are no specific concerns. In contrast, the analyses suggest that heavy metals may be built up over long periods of irrigation with dairy effluent in soils, and then transported to the groundwater in the presence of EDTA. However, more research would be required to clarify this matter.

year: 2009

title: Obituary – Allan Edward Hewitt. In memory of Dr Allan Edward Hewitt - a multi-talented soil scientist

authors: Aislabie, J

subjects: obituary

abstract: Allan is remembered fondly by his colleagues in soil science throughout New Zealand and his Manaaki Whenua co-workers especially those in our Dunedin and Lincoln offices.

text: Obituary – Allan Edward Hewitt. In memory of Dr Allan Edward Hewitt - a multi-talented soil scientist Allan is remembered fondly by his colleagues in soil science throughout New Zealand and his Manaaki Whenua co-workers especially those in our Dunedin and Lincoln offices.

year: 2022-05-18

title: Phytoplankton nutrient limitation in Lake Rotorua

authors: Tempero, Grant Wayne

abstract: Lake Rotorua is one of 12 lakes jointly managed by the Rotorua Lakes Council, Te Arawa Lakes Trust and the Bay of Plenty Regional Council under the Rotorua Te Arawa Lakes Programme. The lake is currently classified as eutrophic and a Trophic Lake Index (TLI) value of 4.2 has been set as an integrated target for lake water quality. A number of catchment and lake management strategies have been implemented to achieve the targeted TLI including land use changes, wetland enhancement, lake weed harvesting, sediment detainment bunds, sewage reticulation and alum dosing. Alum (aluminium sulphate) is commonly applied to freshwater and wastewater systems to remove phosphorus, reducing its availability for phytoplankton growth. The initiation of alum dosing to the Utuhina Stream in 2006 and the Puarenga Stream in 2010 was associated with a significant decline in water column dissolved reactive phosphorus (DRP) and improvements in water quality of Lake Rotorua. 
The use of alum to control external and internal phosphorus loading has been identified as key component in the restoration of Lake Rotorua and recently observed improvements in water quality suggest that the lake could be transitioning to a more phosphorus limited state. Determination of phytoplankton nutrient limitation in Lake Rotorua was identified as a priority through the 2017 Plan Change 10 Science Review. An initial seasonal nutrient limitation study was carried out in 2019 with nutrient limitation assays conducted at 3-monthly intervals over the course of the year. Nitrogen limitation was indicated for the March assay and nutrient co-limitation for the December period, but results for the winter and spring periods were inconclusive. There has also been increasing recognition that nutrient availability in limnetic systems may vary in response to seasonal changes in external and external loading and even to isolated storm events. 
The University of Waikato was contracted to investigate potential changes in nutrient limitation within Lake Rotorua at sub-monthly time-scales, and to determine if alum dose rates could be optimised to take advantage of periods of phosphorus limitation. Phytoplankton nutrient limitation growth assays were conducted on a fortnightly basis from mid-October 2020 to May 2021. In addition to determination of lake surface nutrient and chlorophyll a concentrations, triplicate 1 L phytoplankton samples were spiked with either phosphorus (0.1 mg-P L⁻¹), nitrogen (1 mg-N L⁻¹) or phosphorus (0.1 mg-P L⁻¹) and nitrogen (1 mg-N L⁻¹) and incubated for 5-days under a single light intensity of 100 μmol m⁻²s⁻¹ PAR at lake surface temperature and photoperiod. Phytoplankton growth responses were measured as comparative chlorophyll a, comparative biomass and net biomass growth. Summarised results from the 16 assays along with the predicted nutrient state from the stoichiometric mass ratio of TN:TP are presented in the table below. 
Under the test conditions nitrogen limitation was indicated for most of the summer months (December–March) and nutrient co-limitation during the spring and late autumn. Only short (~2 weeks) periods of P-limitation were observed, one of which was associated with an intensive storm event at the end of March. These seasonal fluctuations in nitrogen and phosphorus supply are similar to those observed in other temperate limnetic systems. In the spring, external nitrogen and phosphorus loading is high, then decline in the summer as rainfall and associated inflows wane. During the summer, internal loading becomes more important in polymictic lakes due to repeated internal nutrient cycling from stratification and mixing events. This results in phosphorus limitation in the spring, transitioning to nitrogen limitation or colimitation (primarily nitrogen) in the summer, and then returning to phosphorus/colimitation during the winter due to increased nitrogen-loading from the catchment from increased catchment discharge. 
Due to the modest periods of phosphorus limitation indicated by the assays, there appears to be little potential for optimisation of alum dose rates in order capitalise on natural periods of phosphorus limitation. Further, changes in phytoplankton community composition and abundance appear to be more strongly driven by physical environmental factors such as temperature, light and wind speed, than nutrient availability. Although alum dosing is effective in removing DRP from the Utuhina and Puarenga inflows, its assumed effectiveness in reducing internal phosphorus loading in Lake Rotorua requires further evaluation.

text: Phytoplankton nutrient limitation in Lake Rotorua Lake Rotorua is one of 12 lakes jointly managed by the Rotorua Lakes Council, Te Arawa Lakes Trust and the Bay of Plenty Regional Council under the Rotorua Te Arawa Lakes Programme. The lake is currently classified as eutrophic and a Trophic Lake Index (TLI) value of 4.2 has been set as an integrated target for lake water quality. A number of catchment and lake management strategies have been implemented to achieve the targeted TLI including land use changes, wetland enhancement, lake weed harvesting, sediment detainment bunds, sewage reticulation and alum dosing. Alum (aluminium sulphate) is commonly applied to freshwater and wastewater systems to remove phosphorus, reducing its availability for phytoplankton growth. The initiation of alum dosing to the Utuhina Stream in 2006 and the Puarenga Stream in 2010 was associated with a significant decline in water column dissolved reactive phosphorus (DRP) and improvements in water quality of Lake Rotorua. 
The use of alum to control external and internal phosphorus loading has been identified as key component in the restoration of Lake Rotorua and recently observed improvements in water quality suggest that the lake could be transitioning to a more phosphorus limited state. Determination of phytoplankton nutrient limitation in Lake Rotorua was identified as a priority through the 2017 Plan Change 10 Science Review. An initial seasonal nutrient limitation study was carried out in 2019 with nutrient limitation assays conducted at 3-monthly intervals over the course of the year. Nitrogen limitation was indicated for the March assay and nutrient co-limitation for the December period, but results for the winter and spring periods were inconclusive. There has also been increasing recognition that nutrient availability in limnetic systems may vary in response to seasonal changes in external and external loading and even to isolated storm events. 
The University of Waikato was contracted to investigate potential changes in nutrient limitation within Lake Rotorua at sub-monthly time-scales, and to determine if alum dose rates could be optimised to take advantage of periods of phosphorus limitation. Phytoplankton nutrient limitation growth assays were conducted on a fortnightly basis from mid-October 2020 to May 2021. In addition to determination of lake surface nutrient and chlorophyll a concentrations, triplicate 1 L phytoplankton samples were spiked with either phosphorus (0.1 mg-P L⁻¹), nitrogen (1 mg-N L⁻¹) or phosphorus (0.1 mg-P L⁻¹) and nitrogen (1 mg-N L⁻¹) and incubated for 5-days under a single light intensity of 100 μmol m⁻²s⁻¹ PAR at lake surface temperature and photoperiod. Phytoplankton growth responses were measured as comparative chlorophyll a, comparative biomass and net biomass growth. Summarised results from the 16 assays along with the predicted nutrient state from the stoichiometric mass ratio of TN:TP are presented in the table below. 
Under the test conditions nitrogen limitation was indicated for most of the summer months (December–March) and nutrient co-limitation during the spring and late autumn. Only short (~2 weeks) periods of P-limitation were observed, one of which was associated with an intensive storm event at the end of March. These seasonal fluctuations in nitrogen and phosphorus supply are similar to those observed in other temperate limnetic systems. In the spring, external nitrogen and phosphorus loading is high, then decline in the summer as rainfall and associated inflows wane. During the summer, internal loading becomes more important in polymictic lakes due to repeated internal nutrient cycling from stratification and mixing events. This results in phosphorus limitation in the spring, transitioning to nitrogen limitation or colimitation (primarily nitrogen) in the summer, and then returning to phosphorus/colimitation during the winter due to increased nitrogen-loading from the catchment from increased catchment discharge. 
Due to the modest periods of phosphorus limitation indicated by the assays, there appears to be little potential for optimisation of alum dose rates in order capitalise on natural periods of phosphorus limitation. Further, changes in phytoplankton community composition and abundance appear to be more strongly driven by physical environmental factors such as temperature, light and wind speed, than nutrient availability. Although alum dosing is effective in removing DRP from the Utuhina and Puarenga inflows, its assumed effectiveness in reducing internal phosphorus loading in Lake Rotorua requires further evaluation.

year: 2022