Water quality improved by application of modified zeolite
September 2010: This is a summary of modified zeolite research conducted between 2004 and 2010. Modified zeolite, developed at Scion and marketed under the name Aqual P by Minsorb (a wholly-owned subsidiary of Blue Pacific Minerals) has potential to improve the quality of waterways and lakes in both New Zealand and overseas.
The problem of excess phosphorus (P) loads in lakes occurs world-wide. For example, 51% of over 14,000 lakes (greater than one hectare in size) in Great Britain were likely to require phosphorus reduction measures to meet water quality standards. Some New Zealand lakes and waterways, especially those surrounded by farmland, require phosphorus reduction. In addition to lakes and waterways, commercial potential exists for these materials in the treatment of drinking water and irrigation reservoirs, domestic and commercial fish ponds and aquaria, golf course ponds, farm dams and troughs, water storage systems in nurseries, aquaculture and swimming pools.
Phosphates and nitrates are major problems in lakes and waterways and can encourage algal blooms. Lake sediments contain a large pool of phosphorus and nitrogen (Özkundakci and Hamilton, 2007). The higher the nutrient concentration – the more eutrophic (nutrient rich) a lake is. The most degraded lakes are classified as hypertrophic.
Zeolites are naturally-occurring minerals whose crystalline structure is in a honeycomb lattice. Found world-wide, their properties can differ markedly between locations. In the Rotorua / Taupo region, zeolites were formed around 250,000 years ago. Intense volcanic activity generated massive ash showers which were eroded in to lakes forming clay sediment beds. Subsequent subsurface heating transformed these clays into highly-porous zeolite rocks.
These North Island zeolites have a unique chemical structure which gives them a high negative charge (cation exchange capacity typically greater than 100 meq/100g) on their surface. Positively charged cations such as ammonium are attracted to the zeolites’ surface and can be absorbed in to the latticework. Due to a fine pore structure, these zeolites have a large specific area for nutrient adsorption.
Research undertaken between 2004 and 2010 by Scion altered the ionic properties of naturally-occurring local zeolites. This modified zeolite has been developed, tested in the laboratory and trialled in natural lakes within New Zealand.
Modified zeolites can be applied to lake and other waterways to remove nutrients. These modified zeolites have advantages (compared to other materials) in removal of phosphates from lakes, including:
- High efficiency means less material required for phosphate removal
- Removal of other prominent pollutants, including ammonia
- New Zealand has sources of zeolite (and they are close to sea ports)
- Potential re-use of bound material with phosphate for fertiliser.
Initial Laboratory studies
The aluminium-modified zeolite developed by Scion gives the natural zeolite (itself a strong cation absorber) a stronger affinity for phosphate. This modified zeolite has the ability to sequester soluble reactive phosphorus and ammonia being released from lake sediments. They can also play a role in coagulating and settling suspended dirt particles, bacteria and many microorganisms that possess charged surfaces in natural water.At Scion, batch incubation studies with nutrients were performed at laboratory scale with artificial and lake waters (Yang et al. 2004). Modified zeolite and pumice samples were treated with different processes to test their efficacy for phosphorus removal. Results showed that both the modified zeolite and pumice samples exhibited substantially higher phosphorus removal capacity than that of natural zeolite or pumice. The modified zeolite performed better than modified pumice and nutrients were strongly (phosphorus irreversibly) bound to the modified zeolite. The next step was to evaluate the relative toxicity of modified zeolite on aquatic species.
Prior to conducting research in a lake, bioassays were undertaken by NIWA (Martin and Hickey, 2007) to determine if modified zeolite had any adverse effects on aquatic species. Across the range of aquatic species tested, the modified zeolite was not found to be harmful to the environment. An exception was for algae which exhibited a toxic response to modified zeolite, the authors attributing this likely to the decrease in phosphorus availability.
Lake Okaro trials
Lake Okaro is a small supertrophic lake south of Rotorua. 90% of its coastline is surrounded by pasture. Due to farming, the levels of nitrogen and phosphorus have increased over the past several decades, resulting in significant algae problems and health warnings during summer periods.The initial field work was conducted in 2006 (Özkundakci, 2006) as a series of mesocosm field studies. Aquatic mesocosms, or experimental water enclosures, are designed to provide a limited body of water with close to natural conditions, in which environmental factors can be realistically manipulated. In this study, 15 mesocosms were deployed in Lake Okaro, treated with different materials.
Lake Okaro: core studies
The efficacy of modified zeolite on blocking the release of phosphorus from lake sediments was evaluated prior to conducting a whole lake trial (Gibbs and Özkundakci, 2010). Two cores were treated with two different grain sizes and dose rates of modified zeolite under both aerobic or anoxic water conditions.The applied modified zeolite had a high affinity for phosphorus with a thin layer (~2mm) completely blocking the release of phosphorus from the sediment under aerobic and anoxic conditions. It also removed phosphorus from the overlying water in contact with the capping layer. Interestingly, it also absorbed mercury and arsenic from the geothermally influenced Lake Okaro sediments. Modified zeolite also completely blocked the release of ammoniacal nitrogen from the sediments as well as ammonia from the water in contact with it.
Two sizes of particles were used, <1mm grain size and 1-3mm particles. The smaller grain sizes were about 50% more efficient than the coarser material in binding phosphorus. The rate of absorption of phosphorus was sufficient to absorb this mineral as it was released from sediment in this lake (and would be adequate for most other lakes in New Zealand and potentially around the world).
Lake Okaro: 2007 application
Over four days in September 2007, Lake Okaro was treated with about 110 tonnes of modified zeolite to form a sediment cap. This modified zeolite was applied where the lake depth exceeded 5 m, equivalent to 20 ha of lakebed. Environment Bay of Plenty contracted NIWA to independently evaluate the efficacy of modified zeolite as a phosphate-inactivation agent and to identify any adverse effects (Gibbs et al., 2007). Their results demonstrated the modified zeolite applied as a capping agent is capable of blocking phosphorus released from the sediment and overlying water.Despite the rapid reduction in lake water total phosphate following modified zeolite application, the trophic state level of the lake remained constant (Özkundakci et al. 2010b). The observed significant decline in P concentration in the bottom waters of Lake Okaro in response to the modified zeolite application suggests that sediment capping was the most effective amongst all of the restoration procedures carried out in this lake, which included a constructed wetland, farm nutrient management, and the riparian restoration.
A follow-up study in 2009 (Gibbs, 2009) showed the modified zeolite adsorbed about 50% of the available phosphorus in the sediment over 18 months from the September 20017 application. The P content in the sediment declined from 3.15g m-2 to around 1.5 g m -2 a reduction of around 50%. Measuring the P content of modified zeolite granules recovered from the lake indicated that most of the P reduction could be attributed to uptake by the modified zeolite.
The researchers speculated that the large grain size of the modified zeolite sank in to the sediment and effectively was only able to remove P from the sediment surrounding it. A further trial in 2009 used a smaller grain size and was expected to result in a more effective sediment cap.
The 2007 sediment capping of Lake Okaro using modified zeolite did not have any undesirable effect on zooplankton or phytoplankton community structure (Özkundakci, et al. 2009). In the long term, the zooplankton community is expected to change in composition with a reduction in nutrients and algal levels. Modified zeolite application had no effect on fish health in Lake Okaro (Landman and Ling, 2010).
Lake Okaro: 2009 application
In a second application in August 2009, the lake was treated with a further 44 tonnes of modified zeolite applied as a slurry (Gibbs, 2009). This application had a finer grain size (0.3-0.5mm) compared with the 2007 application (1-3mm). This fine grain size was able to absorb phosphorus from the water column, possibly a function of the lower settling rate. Results have not yet been reported on the efficacy of this application of modified zeolite as a sediment cap. There was strong evidence that the finer modified zeolite slurry acted as a flocculant as it precipitated organic matter, including algae out of the water.
Lake Rotorua trials
As part of the programme for the restoration of Rotorua lakes, Environment Bay of Plenty studied the use of sediment capping materials to reduce the amount of dissolved reactive phosphorus in the lake water column from sediment release. Of four P-inactivation products trialled (Gibbs et al. 2008), modified zeolite had a high P-binding rate and was the only capping material which reduced the released of ammonia nitrogen from the sediments.The potential for modified zeolite as a sediment cap in Lake Rotorua has been trialled. Laboratory trials by NIWA and the University of Waikato (Gibbs and Hamilton, 2009) compared modified zeolite with two other potential sediment cap materials. All three performed well in the lab and suggested no phosphorus would be released from sediments following application of these capping materials.
The Bay of Plenty Regional Council has currently contracted NIWA to undertake further lab trials testing the effect of Aqual P and other sediment locaking agents on aquatic fauna to confirm environmental safety. The Regional Council has tested two different versions of Aqual P in lake trials and has developed application techniques for making precision applications. This is in response to the challenge that uneven application of the modified zeolite occur on the lake bottom due to lake depth, drifts and currents. In 2011 an aerial application to lake Rotoiti's Okawa Bay stopped a developing algal bloom.
Published research on this modified zeolite in New Zealand
Martin, M.L., Hickey, C.W. 2007. Scion Zeolite Bioassays. NIWA Client Report HAM2007-030.
Gibbs, M. 2009. Lake Okaro re-treatment with Z2G1 in August 2009. NIWA Client Report: HAM2009-177.
Gibbs, M., Bremner, D., van Kooten, M., Ozkundakci, D. 2008. Comparison of efficacy of four P-inactivation agents on Lake Rotorua sediments. NIWA Client Report: HAM2008-105.
Gibbs, M., Dudli, S., Vopel, K., Hickey, C., Wilson, P., Ozkundakci, D. 2007. P-inactivation efficiency of Z2G1 as a capping agent on Lake Okaro Sediment. NIWA Client Report: HAM2007-112.
Gibbs, M., Hamilton, D. 2009. Sediment Capping in Lake Rotorua. Consultation Meeting Rotorua 16 April, 2009.
Gibbs, M., Özkundakci, D. 2010. Effects of a modified zeolite on P and N processes and fluxes across the lake sediment–water interface using core incubations. Hydrobiologia DOI:10.1007/s10750-010-0358-9.
Özkundakci, D., 2006. Efficacy of sediment capping materials and flocculants for nutrient removal as a lake restoration technique – Case study on Lake Okaro, New Zealand. Diplom thesis, Lippe and Hoxter University of Applied sciences, Hoxter, 202 pp.
Özkundakci, D., 2010. Speciation and dynamics of phosphorus in relation to lake restoration methods. Ph.D. thesis, Department of Biological Sciences, University of Waikato. 10.1007/s10750-009-0071-8
Özkundakci, D., Hamilton, D. 2007. Recent studies of sediment capping and flocculation for nutrient stabilisation. CBER Report 53. Report prepared as part of the Lake Ecosystem Restoration New Zealand (LERNZ).
Özkundakci, D., Hamilton, D.P. and Gibbs, M. 2010a. Hypolimnetic phosphorus and nitrogen dynamics in a small, eutrophic lake with a seasonally anoxic hypolimnion. Hydrobiologia DOI:10.1007/s10750-010-0358-9.
Özkundakci, D., Hamilton, D.P., Scholes, P. 2010b. Effect of intensive catchment and in-lake restoration procedures on phosphorus concentrations in a eutrophic lake. Ecological Engineering 36: 396-405.
Özkundakci, D., Duggan, I.C., and Hamilton, D.P. 2009. Does sediment capping have post-application effects on zooplankton and phytoplankton? Hydrobiologia 10.1007/s10750-009-9938-y.
Yang, Z., van den Heuvel, M.R., Stuthridge, T.R. 2004. Assessment of the performance of nutrient reduction treatments for the Rotorua Lakes. Contract R02445. Prepared for Environment BOP.