TREATMENT OF LANDFILL LEACHATE USING ZEOLITE

Transcription

1 TREATMENT OF LANDFILL LEACHATE USING ZEOLITE Grant Redvers and Renate Timm (City Design Ltd), Garry Peters (Auckland City Council) and Craig Mowatt (NZ Natural Zeolite Ltd) Introduction City Design Ltd, on behalf of Auckland City Council Utility Planning Department, have been investigating treatment options for treating landfill leachate discharging from landfills within Auckland City. As part of this investigation the use of zeolite, a naturally occurring clay mineral, has been explored for it s potential to remove contaminants of concern from leachate sources. Ammonia nitrogen (NH 3 + and NH 4 + ) is often a contaminant of particular concern in landfill leachate as it is known to have the potential to promote eutrophication and to cause toxic effects on aquatic organisms in receiving waters (Nguyen and Tanner, 1998). Zeolite has been shown to have a high cation exchange capacity (CEC) (Bolan, 1998) with a particular affinity for ammonium (NH 4 + ) ions (Nguyen and Tanner, 1998). This property has led to the investigation of using zeolite for treating a range of agricultural wastewater including dairy, piggery and wool scour effluents (Blennerhassett, 1996). The application of zeolite to treat landfill leachate has been investigated by City Design in conjunction with NZ Natural Zeolite, a subsidiary of Resource Refineries Ltd. The investigation has involved pilot treatment plant trials at Meola Closed Landfill in Auckland City. The primary objective of the investigation was to assess the potential for zeolite to remove ammonia nitrogen (NH 3 +NH 4 ) from landfill leachate. Methods General sampling methods The investigation involved two field trials using a pilot treatment plant (Figure 1). The plant consisted of three treatment columns, each containing 0.3m 3 zeolite, through which leachate was pumped in series or in parallel. Trial 1 Trial 1 was run for a duration of 12 hours. Samples were collected at the start of the trial and every hour thereafter from the influent and from each of the three treatment columns (A, B and C), column C being the final treated effluent. Leachate was pumped through the treatment columns in series at a flow rate of 18L/min. Approximately 0.9m 3 (0.3m 3 per column) of zeolite was used for the trial.

2 Figure 1: Pilot zeolite treatment plant set up at Meola Closed Landfill. Each sample was analysed for ammonia (NH 3 +NH 4 ) and iron. In addition, a raw leachate sample and two samples of the final treated effluent were analysed for a range of trace metals, major cations, volatile organic compounds (VOC s) and semi-volatile organic compounds (SVOC s). Trial 2 Trial 2 was run for a duration of 36 hours using only one treatment column. The longer trial duration and use of only one treatment column (0.3m 3 zeolite) was to ensure that the zeolite became fully loaded with ammonia in order to assess the total absorption capacity. Samples were collected at the start of the trial and every three hours thereafter from the influent and the treated effluent (after passing through one column only). Leachate was pumped through the treatment plant at a flow rate of 18L/min. Each sample was analysed for ammonia and iron. In addition, samples were analysed for conductivity and major cations every 9 hours. A sample of the loaded zeolite was also analysed for a range of trace metals, nutrients, VOC s and SVOC s. Analytical Methods All raw and treated leachate samples were sent to Watercare Laboratory Services Ltd for analysis. Samples were analysed in accordance with Standard Methods (APHA AWWA, 1998). Samples of raw and loaded zeolite were sent to Watercare Laboratory Services and Hill Laboratories for analysis for nutrients, trace metals, major cations, SVOC s and VOC s.

3 Watercare samples were analysed using Standard Methods. Hill's samples were analysed to determine the water extractable levels of ammonium-nitrogen, phosphorus, potassium, calcium, magnesium and iron. In-house methods were used for these analyses, involving a water extraction and ICP-OES determination. Results and Discussion Trial 1 Table 1 summarises the results for Trial 1. The results for Na, Ca, Mg and K show the removal efficiency at the initiation of the trial (time 00:00) whereas the ammonia and iron results represent the average removal efficiency over the duration of the trial. Table 1: Removal efficiencies for Trial 1. Ammonia Fe Na Ca Mg K Raw Treated % removal 86% 69% 30% 83% 3% 73% Ammonia removal of greater than 99 percent was achieved in the final treated effluent at the start of Trial 1, reducing to 71 percent removal after 12 hours (Figure 2) Col A Col B Col C Ammonia (% removal) :00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 Time (hh:mm after initiation of test) Figure 2: Percent removal of ammonia achieved from each treatment column over time. At the conclusion of Trial 1, the ammonia concentration of the final treated effluent was still significantly lower than that of the raw effluent (Figure 3). The absorption efficiency of Column A declined more rapidly than the other two columns. This was expected as Column A received the most concentrated leachate inputs. The Column A curve has been extrapolated (Figure 3) to estimate the potential breakthrough time (i.e. the time at which the zeolite becomes fully loaded with

4 ammonia). Results suggest that at the flow rate of 18 L/min and using 0.3m 3 of zeolite, it would take longer than 24 hours for breakthrough to occur Ammonia :00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 Time (hh:mm after initiation of test) 18:00 Raw Col A Col B Col C Log. (Col A) Figure 3: Ammonia concentration in raw leachate and in effluent from each treatment column over time. Results of Trial 1 show that iron, sodium, calcium and potassium were also removed from the raw leachate to varying degrees (Table 1). However, high concentrations of these cations in raw leachate may reduce the absorption of ammonia due to preferential binding (Bolan N.S., 1998). Magnesium was not absorbed to the same degree as the other cations. SVOC s and VOC s were generally below detection limits in the raw leachate, therefore no assessment can be made of the removal capabilities of zeolite in relation to organics. Trial 2 Ammonia removal of almost 80 percent was achieved at the start of Trial 2, reducing to less than zero after 33 hours (i.e. breakthrough was reached, when the concentration of ammonia in the treated effluent was slightly higher than that in the raw leachate) (Figure 4). 00:00

5 Ammoina (% removal) :00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 24:00:00 27:00:00 30:00:00 33:00:00 36:00:00 Time (hh:mm after initiation of test) Figure 4: Percent removal of ammonia over time. The point of breakthrough can be seen in Figure 5 where the treated effluent curve overlaps the raw leachate curve after a duration of 33 hours. After this point it would be expected that the two curves would continue to periodically cross paths Ammonia Raw Leachate 10 Treated Effluent Log. (Treated Effluent) 0 00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 24:00:00 27:00:00 30:00:00 33:00:00 36:00:00 Time (hh:mm after initiation of test) Figure 5: Ammonia concentration in raw and treated effluent over time.

6 Zeolite Samples Raw and loaded zeolite samples were analysed for nutrients, trace metals, major cations, VOC s and SVOC s. Samples were analysed for total load by Watercare Laboratory Services and for readily available load by Hills Laboratories (Table 2). The later analysis, using a weak water leaching extraction, was undertaken in an effort to assess the amount of nutrients that would be readily available to plants. Table 2: Results of zeolite analysis for Trail 2. Ammonia Fe Na Ca Mg K Raw Loaded (total) Loaded (water extraction) Results indicate that although a considerable amount of iron and ammonia were absorbed by the zeolite, only a small proportion of these cations were extracted by the water leaching extraction procedure. However, water soluble nutrient levels are often not related to exchangeable nutrient levels. Based on other, similar types of experiments (Mowatt, pers com.) the ammonia, calcium, sodium, potassium and iron ionically absorbed by the zeolite would be expected to significantly contribute to the nutrient pool if the saturated zeolite was added to a growing medium or sand based sports turf carpet The amount of iron measured in the raw zeolite sample (4640 mg/kg) was thought to have been artificially elevated due to relatively high iron concentrations in the wash water used in the refining process. Comparison of Trial 1 and Trial 2 Results The ammonia removal efficiency for Trial 2 can be compared to the removal efficiency reported for column A in Trial 1. A similar level of ammonia removal was achieved after 12 hours for both trials. The longer duration of Trial 2 confirmed the estimated point of breakthrough extrapolated from the results of Trial 1. The level of iron removal for Trial 2 was consistent with the levels achieved in Trial 1. However, removal levels for sodium, calcium, magnesium and potassium were all less for Trial 2. VOC s and SVOC s were not analysed for Trial 2 due low results recorded for Trial 1. Conclusions Zeolite can successfully remove ammonia nitrogen from Meola landfill leachate. Iron and other cations (particularly sodium, calcium and potassium) are also removed from the leachate to varying degrees;

7 Future Developments The long term environmental and economic sustainability of using zeolite to treat landfill leachate has yet to be determined. Identifying and developing a secondary use for the loaded zeolite material will be a crucial factor in determining sustainability. Use of the loaded zeolite as an additive to potting mix and as a fertiliser is therefore under investigation. 1. Plant Growth Trials Plant growth trials are currently being undertaken by NZ Natural Zeolite using loaded zeolite from the second field trial. In one trial broccoli seedlings were transplanted into a mix containing Meola zeolite added at 10% (v/v) with a nutrient deficient organic media and several standard potting mixes. Results indicated that loaded zeolite from Meola grew plants almost as well as the standard growing mixes. Any nutrient deficiencies could easily be resolved by addition of the appropriate fertiliser. The possibility of using loaded zeolite from Meola as an additive to potting mixes would enhance the economics of using the material as a solution for the Meola leachate treatment programme. 2. Fertiliser Trials Investigation into the potential to use loaded zeolite for a sports field fertiliser/conditioner have been undertaken by NZ Natural Zeolite and Auckland City Council (Recreation and Community Services - RACS). The initial outcome of these investigations has determined that under-sowing methods will not be suitable at most sports fields in Auckland City due to rocks at depth under the turf of most fields. Other options include using zeolite as a topdressing type fertiliser/soil amendment. Whilst RACS are also concerned about pathogens possibly associated with the loaded zeolite preliminary tests have indicated that this will not be a problem. Literature examining the association between zeolite and pathogens indicates that pathogen populations decline when in contact with zeolite. None-the-less, further testing to assess potential human health risks is required. The New Zealand Sports Turf Institute supports the use of zeolite as a turf conditioner / fertiliser. Zeolite has been added to the turf at both Wellington and Waikato stadium playing areas where it increases moisture holding capacity and nutrient holding capacity making management far easier. Zeolite is now routinely added to sand based golf greens. NZ Natural Zeolite are also currently investigating loading zeolite from other nutrient sources to use as slow release fertilisers for both the organic and conventional markets. 3. Treatment Plant Design A comprehensive financial cost model for the treatment of leachate at Meola Closed Landfill is currently under development. If zeolite treatment is confirmed to be cost effective design of a full-scale pilot treatment plant will be undertaken. References APHA AWWA (1998) Standard Methods for the Examination of Water and Wastewater, 20 th edition. American Public Health Association, American Water Works Association.

8 Blennerhassett J (1996) An investigation into the use of zeolites for removing ammonium and potassium ions from dairy, piggery and wool scour effluents. Unpublished honours thesis, Department of Soil Science, Massey University, Palmerston North. Bolan N S (1998) Ammonium retention by zeolite from tannery effluents. Fertiliser and Lime Research Centre, Institute of Natural Resources, Massey University, Palmerston North. Nguyen M L and Tanner C C (1998) Ammonium removal from wastewaters using natural New Zealand Zeolites. New Zealand Journal of Agricultural Research, 41: