Improving multi-soil-layer (MSL) system remediation of dairy effluent

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1 ecological engineering 32 (2007) 1 10 available at journal homepage: Improving multi-soil-layer (MSL) system remediation of dairy effluent R. Pattnaik a, R.S. Yost a,, G. Porter a, T. Masunaga b, T. Attanandana c a Department of Tropical Plant and Soil Sciences, University of Hawai i, 3190 Maile Way, 102 St. John, Hawaii 96822, USA b Faculty of Life and Environmental Science, Shimane University, Matsue , Japan c Department of Soil Science, Faculty of Agriculture, Kasetsart University, Jatujak, Bangkok 10900, Thailand article info abstract Article history: Received 23 December 2006 Received in revised form 5 July 2007 Accepted 16 August 2007 Keywords: Dairy effluent Dairy wastewater treatment Multi-soil-layer system Soil dynamics Tropical soils Inorganic nitrogen removal effectiveness Phosphate removal effectiveness Dairy effluent disposal is a serious problem in the Hawaiian Islands. Dairies often establish multiple settling lagoons to accumulate and store effluent. Occasionally, the overflow of lagoons leads to the transfer of nutrients, such as nitrogen (N) and phosphorus (P), and other contaminants, to hydrologically associated surface, subsurface, and coastal waters. This study was conducted to assess the removal of inorganic N and phosphate in dairy effluent using multi-soil-layer (MSL) systems. Four MSL systems were constructed with two replications of two treatments, which were Perlite and the Leilehua soil. Both materials were used separately for forming an aerobic layer in the MSL systems, whereas an anaerobic layer was formed from a mixture of charcoal, sawdust, iron filings and Honouliuli soil. The results of this study revealed that the removal of inorganic N was similar for the Leilehua and Perlite MSL system, which was 22 93% and 21 96%, respectively. Phosphate removal was higher in the Leilehua MSL system (64 99%) compared to the Perlite MSL system (9 97%). Additional aeration increased the removal of phosphate by the Leilehua MSL system. Sucrose application with a constant rate of aeration increased the removal of inorganic N both in the Leilehua and Perlite MSL systems and increased phosphate removal in the Perlite MSL system. The study demonstrated that MSL systems have the potential to remove high percentages of inorganic N and phosphate in dairy effluent enabling reuse of the water Elsevier B.V. All rights reserved. 1. Introduction The dairy industry generates wastewaters characterized by high concentrations of nutrients, organic contents, and pathogens (USDA-SCS, 1992). The organic and nutrient content of dairy wastewaters depends upon the size, lactation, and diet of the cow. In addition, dairy wastewater composition is significantly influenced by the wastewater management, climate, operating conditions, and types of flushing. Table 1 shows the levels of major nutrients in dairy wastewater. The dairy industry is one of the major sources of waste efflu- ents in Hawaii and in the Continental U.S. (USDA-SCS, 1992). Dairy effluent disposal is a serious problem in Hawaii and other Pacific Islands (Farrell-Poe, personal communication, 2007). The problem is due to the confined aquifers and limited availability of water in Pacific Island environments. The current method used in Hawaii to dispose dairy effluent is large settling lagoons. Dairies often establish multiple lagoons to accumulate and store effluent. Occasionally, the lagoons overflow, leading to the transfer of nutrients, such as nitrogen (N) and phosphorus (P), and other contaminants, which can pollute surface, subsurface, and coastal waters. Effluents Corresponding author. Tel.: ; fax: address: rsyost@hawaii.edu (R.S. Yost) /$ see front matter 2007 Elsevier B.V. All rights reserved. doi: /j.ecoleng

2 2 ecological engineering 32 (2007) 1 10 Table 1 Dairy wastewater characteristics (Wright, 1996) Potential pollutant source Biochemical oxygen demand (mg L 1 ) Nitrogen (mg kg 1 ) Phosphorus (mg kg 1 ) Volume gallons (100 cows y 1 ) Milking center waste , ,000 Silage leachate 12,000 90, ,000 Barnyard runoff , ,000 Dairy manure 20, ,000 high in N and P concentration can cause eutrophication of the receiving waters, degrading water quality (Smith et al., 1999). The Environmental Protection Agency (EPA) and State Department of Health (DOH) have rules and regulations for the disposal of dairy effluent (Hawaii State Department of Health Wastewater Branch, 1996). Proper management of dairy effluent is currently a serious problem in Hawaii, which has increased the operation costs and reduced profitability of many island dairies. The inability of many dairy operators to properly manage the effluent has forced more than 50% of them to close during the last 10 years (C.N. Lee, personal communication, 2006). With rising environmental concerns and tighter governmental regulations, managing animal wastes in an environmentally responsible and economically feasible way can be a challenge. It is becoming imperative that new ways of waste treatment be found that reduce excessive nutrients from dairy effluent and yet are efficient and reliable. Some of the methods of dairy waste treatment include land application (Caro-Costas et al., 1972; Valencia-Gica et al., 2004), vegetative filter strips (Ikenberry and Mankin, 2000), constructed wetlands (Schaafsma et al., 2000), aerobic and anaerobic processes (Manariotis and Grigoropoulos, 2003), and bioremediation (Prochaska and Zouboulis, 2003) which have performed well, but their widespread use is limited because they are either costly, require regular maintenance, require large areas of land, or the wastewater must be pre-treated. The multi-soil-layer (MSL) system is a promising alternative with potential for reducing contamination associated with dairy effluent. The MSL system is a technology that uses natural soil in a unit to facilitate wastewater treatment (Wakatsuki et al., 1993). This has been successfully developed in Japan and Thailand to treat domestic and restaurant wastewater as well as polluted river water (Wakatsuki et al., 1993; Luanmanee et al., 2001). The system reduces levels of inorganic contaminants such as nitrate, ammonium, and phosphate, as well as organic contaminants as measured by high COD (chemical oxygen demand) and BOD (biological oxygen demand). This is a biphasic layered system that uses locally available materials such as soil, iron particles, jute or sawdust, charcoal, and zeolite or alternative materials (Attanandana et al., 2000; Luanmanee et al., 2001). Two layers that comprise MSL systems are aerobic and anaerobic. Aerobic layers consist of zeolite or Perlite alternated with anaerobic layers of soil mixture blocks. The efficiency of the MSL system in purifying wastewater depends on the relative effectiveness of aerobic and anaerobic layers (Wakatsuki et al., 1993; Attanandana et al., 2000). The aerobic layer enhances nitrification, oxidation and precipitation of mobile ferrous iron to high-surface area ferric oxide, enhancing phosphorus sorption (Wakatsuki et al., 1993). In the anaerobic layer of the soil mixture block, nitrate is transformed into nitrous oxide and nitrogen gas (denitrified) and ferric iron is reduced to the more mobile ferrous iron, which moves out of the anaerobic layer (Wakatsuki et al., 1993). Although an appropriate amount and timing of aeration is necessary (Luanmanee et al., 2002), the maintenance of an MSL system is simple and the effective life of such systems was estimated to be longer than 10 years (Luanmanee et al., 2002). Although various types of wastewater treatments have been treated successfully using the MSL system in Japan and Thailand, to-date, no MSL system has been tested or adapted for the remediation of dairy effluent. In addition, there is not much information available on the reliability, consistency, and nutrient removal efficiency of MSL systems. Thus, it is of interest to determine whether the MSL system can remediate dairy effluent. This study was conducted to (a) investigate the potential of the MSL systems in remediating dairy effluent, (b) compare the removal of inorganic N and phosphate, between MSL systems with the aerobic layers made from Leilehua soil or Perlite, and (c) evaluate the effect of aeration and sucrose additions on inorganic N and phosphate removal efficiency. Table 2 Selected physical properties of Leilehua and Honouliuli soils Series Clay (<0.002) (% of <2 mm mineral soil) Silt ( ) (% of <2 mm mineral soil) Sand (0.05 2) (% of <2 mm mineral soil) Water holding capacity (% of <2 mm mineral soil) 33 kpa 1500 kpa Bulk density (g cm 3 ) Particle density (g cm 3 ) Leilehua n/a Honouliuli Source: Soil Survey Staff (2006).

3 ecological engineering 32 (2007) Materials and methods 2.1. Experimental site and design The experimental site was located in Waianae, latitude 21 27, longitude on the west shore of the island of O ahu, Hawaii. Average maximum and minimum daily temperatures of the area are 28 C (83 F) and 16 C (61 F) (Hobo Weather Station, ). The experiment was conducted using dairy effluent from the third settling lagoon of an effluent waste management system. Four MSL systems were constructed, comprising two treatments with two replications each, arranged in a completely randomized design (CRD). Perlite or Leilehua soil (A horizon, Typic Kanhaplohumult) was used for the aerobic layer in the two treatments. The anaerobic layer for both treatments consisted of a mixture of charcoal, sawdust, iron filings and the Honouliuli soil (A horizon, Typic Chromustert). The physical and chemical properties of both the Leilehua and Honouliuli soils used for the experiment are given in Tables 2 and MSL systems and operations Cross-section composition of the overall MSL systems is presented in Fig. 1. Each of the MSL system consisted of a high-density polyethylene (HDPE) corrugated sewage pipe with 45.7 cm interior diameter by 1 m in height with a crosssectional area of approximately m 2 (Fig. 1). A 25.4 mm PVC pipe was installed at the base of each of the upright HDPE pipe to discharge the MSL treated effluent from the system. A layer of gravel ( 5 cm) was placed at the bottom of the upright pipes to facilitate system discharge. Each system was assembled from seven alternating layers of soil mixture blocks (anaerobic layers) and eight layers of Leilehua soil or Perlite (aerobic layers) (Fig. 1). Each of the soil mixture blocks consisted of Honouliuli soil mixed with finely ground charcoal, fine sawdust, and approximately 1 mm diameter iron filings at the ratio of 7:1:1:1 by dry weight. The soil mixture was evenly mixed using an concrete mixer and packed into two sizes of pre-stitched burlap bags, approximately 5 cm 10 cm 22 cm and 5 cm 10 cm 38 cm. The particle sizes of both the Leilehua soil and the Perlite filler were less than or equal to 4 mm. An aeration pipe was installed approximately 50 cm from the bottom for the subsequent infusion of air whenever it was necessary (Fig. 1). An array of effluent emitters was installed on the top ( 80 cm from the bottom) of the aerobic and anaerobic layers through which the dairy effluent was discharged into the system (Fig. 1) Application rates The dairy effluent was directly pumped from the lagoon, filtered using a m plastic disc filter (140 mesh) to remove the larger particles, and discharged into the MSL system. Three application rates of effluent were applied to the system according to the performance of the system. An initial flow rate of 80 L day 1 (505 L m 2 day 1 ) was applied to each of the system from 18 April to 3 November Effluent was applied through drip irrigation emitters during approximately 20 h day 1. The flow rate was reduced to 40 L day 1 (252 L m 2 day 1 ) on 3 November 2005 and continued until 20 April Then from 20 April to 10 July 2006 the flow rate was again reduced to 28 L day 1 (178 L m 2 day 1 ) Aeration rates Different aeration rates were applied to the systems. Aeration was not applied to the systems until the 10th month of the study. The systems were aerated at a rate of 28 L min 1 from 10 February to 13 April The aeration was increased to 31 L min 1 from 14 to 27 April The aeration rate was decreased to 17 L min 1 for 1 week, from 28 April to 4 May 2006 followed by a rate of 11 L min 1 until 18 May The aeration rate was increased again to 23 L min 1 from 19 May until 10 July Sucrose additions An additional source of carbon in the form of a sucrose solution was applied to the MSL system beginning at the end of the 12th month of the study in attempt to improve system performance. The sucrose solution was calculated based on the amounts needed for a stoichiometric reduction of the expected oxygen content of the MSL system. The percent pore space was calculated first from the bulk densities and particle densities of Leilehua and Honouliuli soil, and Perlite. Then the amount of air space was calculated from the volume of each system. The amount of oxygen was calculated from the amount of air space and the amount of oxygen in the air. The amount of sucrose was calculated based on the stoichiometric reaction equation, which shows how much sucrose is needed for the microorganisms to consume the spe- Table 3 Chemical properties of Leilehua and Honouliuli soils Soil ph (H 2 O, 1:1) OC a (% of <2 mm) TN b (% of <2 mm) Dithionite c (% of <2 mm) Oxalate d (% of <2 mm) P sorbed e (mg kg 1 ) Leilehua Honouliuli n/a 100 Source: Soil Survey Staff (2006). a Organic carbon. b Total nitrogen. c Dithionite-citrate extractable iron. d Ammonium oxalate iron. e Guo and Yost (1998).

4 4 ecological engineering 32 (2007) 1 10 Fig. 1 Cross-sections of the MSL systems (Leilehua and Perlite). cific amount of oxygen: C 12 H 22 O O 2 12CO H 2 O Finally, the application of sucrose was made as a solution mixed with the incoming effluent and applied based on the effluent retention time of the MSL systems. The calculated concentration of sucrose solution was 19 g (0.055 moles per 500 ml) for the Leilehua system and 22 g (0.064 moles 500 ml) for the Perlite system Analytical methods Samples were taken every week except during the period December 2005 to 14 January After filtering samples

5 ecological engineering 32 (2007) Table 4 Dairy effluent used in this experiment, in comparison with data from other dairy lagoons in Hawaii Source ph EC (ms cm 1 ) TSS (mg L 1 ) TN ( gml 1 ) NH 4 + -N ( gml 1 ) NO 3 -N ( gml 1 ) TP ( gml 1 ) IP ( gml 1 ) COD (mg L 1 ) Dairy a a n/a n/a 14.5 n/a n/a Dairy b b n/a n/a This experiment c This experiment d n/a This experiment e f NA EC: electrical conductivity; TSS: total suspended solid; TN: total nitrogen; TP: total phosphorus; IP: inorganic phosphate; COD: chemical oxygen demand. a Analysis of lagoon effluents from various nutrient streams (Fukumoto et al., 2000). b Valencia-Gica et al. (2004). c One month before running the experiment, 3 March d The beginning of the experiment, 2 May e The end of the experiment, 10 July f Total inorganic N (summation of NH 4 + -N and NO 3 -N). were analyzed for the following: ammonia nitrogen (NH 4 + -N), nitrate nitrogen (NO 3 -N), and inorganic phosphate. Ammonia nitrogen was measured using the salicylate method (Mulvaney, 1996a). Nitrate nitrogen was measured using the cadmium reduction method (Mulvaney, 1996b). Total effluent nitrogen consisted of 98% ammonium and about 1% nitrate. The total inorganic nitrogen (Inorganic N) was approximated as the summation of NH 4 + -N and NO 3 -N. The ascorbic acid method was used to measure total inorganic phosphate (Kuo, 1996) Statistical analysis The percentage removal of inorganic N and phosphate between the Leilehua and Perlite MSL systems were compared using Sigma Plot version 9 (Sigma Plot, 2004). Data for selected intervals of time corresponding to specific treatments were also analyzed using the Statistical Analysis Software, SAS PROC MIXED Repeated Measures ANOVA and Least Square means (LSmeans) (SAS, 2004) (Littell et al., 1996, 1998; SAS, 2004). (3) the combination of these two improvements Characteristics of dairy effluent The analysis of the effluent was compared with other dairy effluents in Hawaii (Fukumoto et al., 2000; Valencia-Gica et al., 2004) (Table 4). The concentration of total N, NH 4 + -N, and NO 3 -N was lower in the effluent use in this experiment than the other dairy effluent. This might be a result of using effluent from the third and last settling of the lagoon system, which was more diluted than that from the first lagoon First phase (year 2005) The effectiveness of the MSL systems in removing inorganic N and phosphate was compared over a 6-month period (5 May 5 October) (Figs. 2 and 3). The MSL systems were not significantly different in percentage removal of inorganic N (P > 0.1) (Table 5). However, the percentage removal of inorganic N was significantly differ- 3. Results The percentage removal of inorganic N and phosphate are discussed in two phases. The first phase data occurred from May to October 2005, when the system was operated at constant conditions and the second phase data from January to July 2006, where specific treatments were applied. Although samples were collected in the first phase from October to December 2005, the data were not included in the analysis because of system malfunction. There was a 6-week pause (2 December 2005 to 14 January 2006) between the two phases due to mechanical problems and also due to a suspected build up of biofilms. In the second phase aeration and sucrose additions were compared in an attempt to increase the efficiency of the MSL systems. Three possible improvements were tested in the second phase: (1) effect of increased aeration, (2) effect of sucrose addition with a constant rate of aeration, and Fig. 2 Removal of inorganic N in the Leilehua and Perlite MSL systems as affected by time. In this figure 2D indicates a 2-day pause; 3D a 3-day pause; 6D a 6-day pause; 8D a 8-day pause; 12D a 12-day pause.

6 6 ecological engineering 32 (2007) 1 10 Fig. 3 Removal of phosphate in the Leilehua and Perlite MSL systems as affected by time. In this figure 2D indicates a 2-day pause; 3D a 3-day pause; 6D a 6-day pause; 8D a 8-day pause; 12D a 12-day pause. Fig. 4 Removal of inorganic N in the Leilehua and Perlite MSL systems as affected by sucrose addition and different rates of aeration. Table5 Acomparison of the effect of time and MSL system on inorganic N removal as analyzed by SAS Proc MSL systems Time < MSL systems time ent over time for both the MSL systems (P < ) (Table 5). The non-significant interaction indicates that the MSL systems behaved similarly in percentage removal of inorganic N(P > 0.1) (Table 5). The inorganic N removal by the Leilehua MSL system and the Perlite MSL system ranged from 22 to 93% (LSmean of 61.94) and 21 to 96% (LSmean of 63.40), respectively (Fig. 2). The percentage removal of phosphate was significantly different by both the MSL systems (P < 0.05) (Table 6). The Leilehua MSL system was more effective in removing phosphate than the Perlite MSL system. There was also a significant difference in percentage removal of phosphate over time (P < 0.001) (Table 6). The significant interaction indicates that there was a decrease in percentage removal of phosphate in the Perlite MSL system (P < 0.1) (Table 6). The percentage removal of phosphate by the Leilehua MSL system (64 99%) (LSmean of 92.70) was greater than the Perlite MSL system (9 97%) (LSmean of 59.41) (Fig. 3) Second phase (year 2006) The effect of aeration A comparison was made between no aeration and two different rates of aeration (28 L min 1 and 31 L min 1 )inremoval of inorganic N and phosphate during a sampling period of 19 January to 27 April 2006 (Figs. 4 and 5). The percentage removal of inorganic N was not significantly different between the MSL systems (P > 0.1) (Table 7). There was no significant difference in percentage removal of inorganic N with aeration for both the MSL systems (P > 0.1) (Table 7). The non-significant interaction indicates that the two MSL systems behaved similarly in percentage removal of inorganic N (P > 0.1) (Table 7). The removal of inorganic N by the Leilehua system and the Perlite system ranged from 8 to 61% (LSmean of 29.34) and 10 to 73% (LSmean of 33.10), respectively (Fig. 4). Table6 Acomparison of the effect of time and MSL system on phosphate removal as analyzed by SAS Proc MSL systems Time MSL systems time Fig. 5 Removal of phosphate in the Leilehua and Perlite MSL systems as affected by sucrose additions and different rates of aeration.

7 ecological engineering 32 (2007) Table7 Acomparison of the effect of aeration and MSL system on inorganic N removal as analyzed by SAS Proc MSL systems Aeration MSL systems aeration Table 10 A comparison of the effect of sucrose and MSL system on phosphate removal as analyzed by SAS Proc MSL systems Sucrose MSL systems sucrose Table8 Acomparison of the effect of aeration and MSL system on phosphate removal as analyzed by SAS Proc MSL systems Aeration MSL systems aeration Table 11 A comparison of the effect of different rates of aeration and MSL system on inorganic N removal as analyzed by SAS Proc MSL systems Aeration MSL systems aeration The percentage removal of phosphate was significantly different between the MSL systems (P < 0.01) (Table 8). The Leilehua MSL system was more effective in percentage removal of phosphate than the Perlite MSL system. Changes in aeration resulted in a significant difference in percentage removal of phosphate (P < 0.1) (Table 8). The significant interaction indicates that the MSL systems behaved differently in the removal of phosphate (P < 0.05) (Table 8). The removal of phosphate by the Leilehua MSL system ranged from 42 to 91% (LSmean of 66.64) and was greater than the Perlite MSL system (11 41%) (LSmean of 27.22) (Fig. 5) The combined effect of sucrose with aeration A comparison was made between the non-sucrose and sucrose applications with constant aeration in removal of inorganic N and phosphate from 16 February to 13 April and 25 May to 10 July 2006 (Figs. 4 and 5). The MSL systems were not significantly different in percentage removal of inorganic N (P > 0.1) (Table 9). However, there was a significant increase in percentage removal of inorganic N with sucrose additions for both the MSL systems (P < 0.1) (Table 9). The non-significant interaction indicates that the MSL systems behaved similarly in percentage removal of inorganic N (P > 0.1) (Table 9). The inorganic N removal by the Leilehua and the Perlite MSL system ranged from 9 to 89% (LSmean of 48.77) and 10 to 92% (LSmean of 53.36), respectively (Fig. 4). The MSL systems differed significantly in the percentage removal of phosphate (<0.05) (Table 10). There was no overall significant difference in percentage removal of phosphate with the sucrose application (P > 0.1) (Table 10). However, the significant interaction indicates that the percentage removal of phosphate was increased in the Perlite system (P < 0.1) (Table 10). The removal of phosphate by the Leilehua MSL system ranged from 59 to 93% (LSmean of 76.31) and was more effective than the Perlite MSL system (11 75%) (LSmean of 46.13) (Fig. 5) The effect of different rates of aeration Three different rates of aeration (11 L min 1, 17Lmin 1, and 23Lmin 1 ) were compared in removal of inorganic N and phosphate between a sampling period of 4 May to 10 July 2006 when sucrose was added (Figs. 4 and 5). The MSL system performance was not significantly different in the percentage removal of inorganic N (P > 0.1) (Table 11). There was no significant difference in percentage removal of inorganic N with different rates of aeration between the MSL systems (P > 0.1) (Table 11). The non-significant interaction indicates that the MSL systems behaved similarly in percentage removal of inorganic N (P > 0.1) (Table 11). The removal of inorganic N by the Leilehua and the Perlite systems ranged from 31 to 89% (LSmean of 60.33) and 43 to 92% (LSmean of 62.24), respectively (Fig. 4). There was a significant difference observed in percentage removal of phosphate between the MSL systems (P < 0.1) (Table 12). There was no significant difference in removal of phosphate with different rates of aeration (P > 0.1) (Table 12). The non-significant interaction indicates that the MSL systems behaved similarly in removal of phosphate (P > 0.1) (Table 12). The percentage removal of phosphate by the Leilehua MSL system ranged from 59 to 93% (LSmean of 73.71) was greater than the Perlite MSL system (17 75%) (LSmean of 46.77) (Fig. 5). Table9 Acomparison of the effect of sucrose and MSL system on inorganic N removal as analyzed by SAS Proc MSL systems Sucrose MSL systems sucrose Table 12 A comparison of the effect of different rates of aeration and MSL system on phosphate removal as analyzed by SAS Proc MSL systems Aeration MSL systems aeration

8 8 ecological engineering 32 (2007) 1 10 Fig. 6 The relationship between P sorbed and soil solution P in Leilehua and Honouliuli soil. 4. Discussion 4.1. Performance of the MSL system in removing inorganic N The efficiency of the MSL systems in removing inorganic N from dairy effluent was not significantly different throughout the study (years 2005 and 2006). Both MSL systems used for the aerobic layers, whether Leilehua or Perlite, were similarly effective in removing inorganic N. However, the MSL systems were significantly different in removal of inorganic N over time in The removal rate of inorganic N in effluent decreased over time. We hypothesized the decrease might be due to inadequate aeration in the aerobic layer or decreased microorganism-available carbon in the anaerobic layer and tested this by adding supplemental aeration and sucrose (as a carbon source) in The systems were not significantly different in removal of inorganic N with supplemental aeration. However, the removal of inorganic N was significantly increased in both the MSL systems with the application of sucrose. The increased removal rate was likely due to the additional carbon provided by sucrose applications, which enhanced microbial activity and thus increased the denitrification in both MSL systems. The removal of inorganic N was not significantly different with different rates of aeration in There were some pauses in effluent delivery by the MSL systems in 2005 and sudden drops in removal of inorganic N seemed to related to these pauses Performance of the MSL system in removing phosphate The efficiency of the MSL systems in removing phosphate from dairy effluent varied significantly during the study (years 2005 and 2006). The Leilehua MSL system was consistently more effective in removing phosphate than the Perlite MSL system. This was probably because of the high P sorption capacity of the Leilehua soil in the Leilehua MSL system (1600 gpg 1 soil) (Fig. 6) which adsorbs phosphate from the effluent. The removal of phosphate was significantly decreased over time by the Perlite MSL system in We hypothesized that the decrease in removal of phosphate by the Perlite system might be a result of decreased microorganism-available carbon in the anaerobic layer related to reduced iron movement into the aerobic layer. Supplemental aeration and carbon (as sucrose) were applied in 2006 to increase the efficiency of the MSL systems in removing phosphate. The percentage removal of phosphate was significantly increased with the application of sucrose in the Perlite MSL system. This might be because the additional sucrose carbon increased the activity of microorganisms resulting in more oxygen consumption and enhanced reducing conditions in the anaerobic layer chemically reducing and moving iron into the aerobic layer where it could precipitate as ferric iron and sorb the phosphate in effluent. The hypothesized decrease in microorganism-available carbon in 2005 seems to be supported by the sharp increase in percentage removal of phosphate by the Perlite MSL system with sucrose applications observed in The removal of phosphate was significantly increased with supplemental aeration by the Leilehua MSL system. This might be because of the sufficient aeration in the Leilehua MSL system oxidized ferrous iron to ferric iron in the aerobic layer, leading to higher adsorption of phosphate by the soil colloids. The sucrose application did not increase the already high removal of phosphate in the Leilehua MSL system. The removal of phosphate was not significantly different with different rates of aeration when comparing the two MSL systems in The systems consistently removed phosphate with different rates of aeration. Thus, from the results of supplemental aeration and sucrose applications it appears that the phosphate removal mechanism is likely different between the two MSL systems. The removal of phosphate in the Leilehua MSL system was mainly due to sorption by iron in the aerobic layer, whereas in the Perlite MSL system it appears to be due to three steps, solubilization in the anaerobic layer, movement into the aerobic layer, and precipitation as ferric oxide Use of MSL-treated effluent The Hawaii State Department of Health has three different categories of recycled water R-1, R-2, and R-3 water which are listed in Table 13 with specific criteria (Hawaii State Department of Health, 2002). R-1 is the highest quality recycled water. It has been filtered and disinfected. It can be used in any form of irrigation served by fixed irrigation systems supplied by buried piping for turf and landscape irrigation of golf courses, parks, elementary schools, roadsides, and residential property where managed by an irrigation supervisor (Hawaii State Department of Health, 2002). R-2 is a slightly lower quality recycled water. It is secondary (biologically) treated wastewater that has also been filtered and disinfected (Hawaii State Department of Health, 2002). Its use requires more caution and restrictive controls than R-1 water. R-3 is the least pure class of recycled water. R-3 quality water is wastewater that has been treated to the secondary level. It can only be used for irrigation at places where people rarely go (Hawaii State Department of Health, 2002). The average concentration of NO 3 -N and phosphate, and fecal coliform colonies in MSL-treated effluent of our study is given in Table 14. If we compare our study with the recycled water requirements of State Department of Health in Hawaii, the MSL-treated effluent comes in as R-3 water. MSL-

9 ecological engineering 32 (2007) Table 13 Recycled Water Standards (Hawaii State Department of Health, 2002) Type of recycled water Treatment Recycled water quality Recycled water monitoring R-1 Oxidized a 23 fecal coliform/100 ml Coliform: no more than one sample in any 30-day period Filtered b Nitrate 10 mg L 1 Disinfected c Total phosphorus 1.0 mg L 1 R-2 Oxidized 200 fecal coliform/100 ml Coliform: no more than one sample in any 30-day period Filtered Nitrate 10 mg L 1 Disinfected Total phosphorus 1.0 mg L 1 R-3 Oxidized Secondary Undisinfected a Wastewater in which the organic matter has been stabilized. b The passing of wastewater through natural undisturbed soils or filter media such as sand. c The destruction, inactivation, or removal of pathogenic microorganisms by chemical, physical, or biological means. Disinfection may be accomplished by chlorination, ozonisation, other chemical disinfectants, UV radiation, membrane processes, or other processes. Table 14 Concentrations of MSL-treated effluent NO 3 -N ( gml 1 ) Phosphate ( gml 1 ) Fecal coliform (cfu/100 ml) May October 2005 a Leilehua MSL system 2.15 ± ± ± 1321 Perlite MSL system 3.81 ± ± ± 674 May July 2006 b Leilehua MSL system 2.48 ± ± ± 95 Perlite MSL system 5.04 ± ± ± 53 a First phase of data without aeration and sucrose addition (mean ± S.D., n = 21). b Second phase of data with different rates of aeration and constant rate of sucrose, considered as the optimal management of the system (mean ± S.D., n = 9). treated effluent meets the criteria of nitrate and fecal coliform (May July 2006) of R-2 water and approaches the criteria for R- 1 water. Improvements in efficiency of the type examined in this study are needed to meet the phosphate criteria. In addition a process, such as chlorination is needed to disinfect the treated effluent. 5. Conclusions Results of this study showed that both MSL systems have the potential to remediate dairy effluent. The percentage removal of inorganic N was high and similar in both the MSL systems. The percentage removal of phosphate was high to very high in the Leilehua MSL system and it removed considerably more phosphate than the Perlite MSL system. The supplemental aeration, which was applied in the second phase of the study, did not significantly improve the removal of inorganic N. The removal of phosphate, however, increased in the Leilehua MSL system with additional aeration. Application of sucrose with constant aeration was crucial for removing inorganic N and phosphate. It appears that sucrose additions increased the microbial activity in the MSL systems which helped to increase the removal of inorganic N and phosphate. The sucrose applications have the potential to improve MSL systems treatment efficiency. The installation of MSL systems is simple and basically requires only electricity, freshwater, a constant supply of effluent and a very small amount of land. The materials used in the system are inexpensive and easily obtainable. The MSL-treated effluent approaches R-1 water criteria, with improvements in P removal still needed. Acknowledgement We gratefully acknowledge the USDA T-STAR Program, University of Hawaii for the support of this research. references Attanandana, T., Saitthiti, B., Thongpae, S., Kritapirom, S., Luanmanee, S., Wakatsuki, T., Multi-media-layering system for food service wastewater treatment. Ecol. Eng. 15, Caro-Costas, R., Abruna, F., Figarella, J., Effect of nitrogen rates, harvest interval and cutting heights on yield and composition of stargrass in Puerto Rico. J. Agric. Univ. Puerto Rico 56, Fukumoto, G.K., Duponte, M.W., Lee, C.N., Livestock Industry Partnering for Education and Program Implementation: Nutrient Management Alternatives and Pollution Prevention Planning. Phase I. A report submitted to the State of Hawaii, Governor s Agriculture Coordinating Committee (GACC). Guo, F., Yost, R.S., Partitioning soil phosphorus into three discrete pools of differing availability. Soil Sci. 163 (10), Hawaii State Department of Health Wastewater Branch, The Health State Guidelines for the Treatment and Use of

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