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Bioresource Technology 59 (1997) 163-168 © 1997 Elsevier Science Limited

All rights reserved. Printed in Great Britain 0960-8524/97 $17.00

COMPOSTING OF FISH WASTES IN A FULL-SCALE IN- VESSEL SYSTEM

P. H. Liao , a L. Jones , a A. K. Lau , a S. W a l k e m e y e r , b B. E g a n c & N. H o l b e k c

aDepartment of Chemical & Bio-Resource Engineering, University of British Columbia, 2357 Main Mall, Vancouver, Canada bEcological Resource Consulting, P.O. Box 329, MerviUe, Canada

CPacific Bio-Waste Recovery Society, Campbell River, Canada

(Received 27 May 1996; revised version received 28 October 1996; accepted 7 November 1996)

Abstract This study carried out in a full-scale fish waste corn- posting facility examined the effects on the 'active' stage of composting of two bulking agents (alder and fir), and two amendments (peat moss and vermiculite). The rise in temperature which occurred as composting progressed was accompanied by an increase in ammonia and volatile fatty acid production. This over- all pattern was observed in all four mixes, whereby the concentrations of ammonia and volatile fatty acids increased rapidly and then declined gradually over the course of monitoring. The changes in their concentra- tions over time proved to be a reliable indicator of the progress of the composting process. Ammonia emis- sions from the composting piles were reduced by the additions of peat moss, vermiculite, and alder, in com- parison to the headspace ammonia level for the fir mix. The results indicated that ammonia management during the composting process could be easily accom- plished by the use of suitable amendments or bulking agents. Peat moss and vermiculite were found to be good amendments for fish composting and alder was found to be a good bulking agent. © 1997 Elsevier Science Ltd.

Key words: Fish wastes, composting, bulking agents, amendments, volatile fatty acids, ammonia.

INTRODUC~ON

As a result of a feasibility study that recommended composting as a viable solution to the problems of waste disposal experienced by processing plants and fish farms in British Columbia, Canada, a full-scale composting facility was built on the University of British Columbia's Research Farm on Vancouver Island (Willow, 1992; Holbek & Egan, 1992). Fish wastes in the form of silage from salmon farms, offal from fish processors and salmon farm mortalities are composted. The composting facility consists of four agitated and aerated composting bays, as well as

163

wastewater collection facilities and an odour control unit.

This research study compared the effects of two bulking agents and two amendments on the fish waste composting process. A bulking agent is a material of sufficient size to provide structural support and maintain air spaces within the compost- ing matrix. Bulking agents are important in the composting process in that they affect the pH, car- bon-to-nitrogen ratio, moisture content and air supply for the aerobic bacteria (Golueke, 1991). Thus, bulking agents are important in modulating the microbial degradation process, as well as the ultimate quality of the product and its suitability for use as a fertilizer or soil enhancement. The term 'amendment' refers to materials added to other sub- strates to condition the feed mixture and thereby facilitate the composting process. They are of two types: structural amendments, which serve to reduce bulk weight and increase air voids so as to provide for proper aeration; and energy amendments, which serve to increase the quantity of biodegradable organic material in the mixture.

Since the composition of wood tissue varies from species to species, the decomposition rates of their respective sawdust should also vary considerably. In this regard, it has been reported that hardwood saw- dust is generally more degradable in soil than sawdust produced from softwoods (Allison et al., 1963). Thus, two bulking agents selected for testing were alder chips (a hardwood) and fir sawdust (a softwood). It was anticipated that alder would pro- vide more readily available carbon in the compost mix than fir, and that the composting process would therefore be enhanced by its use.

The amendments tested were peat moss and ver- miculite. Peat moss, like alder, provides a good carbon source. In addition, it is able to increase the cation-exchange capacity of the compost (Mathur et al., 1990). Vermiculite, a three-layered clay mineral, is a novel amendment chosen for its ability to bind potassium ions (Nommik & Vahtras, 1982). Since

164 P. H. Liao, L. Jones, .4. K. Lau, S. Walkemeyer, B. Egan, N. Holbek

potassium and ammonium have very similar ion sizes, it was hypothesized that ammonium could also be locked in by the vermiculite. This would allow for the conservation of nitrogen in the composting mix which would improve its quality as a fertilizer. The accompanying reduction in the release of ammonia gas would be beneficial from odour and air quality control perspectives, each of which poses chronic problems in large-scale composting facilities.

Volatile fatty acids (VFA) and ammonia were used as the major indices of decomposition for the fish-waste composting process (Liao et al., 1995). During the active phase of composting, the concen- trations of ammonia increase as a result of the microbial metabolism of protein. The microbes first metabolize protein to its constituent amino acids, and then deaminate the amino acids to produce fatty acids and ammonia. Fatty acids derived from the deaminization of amino acids, as well as those resulting from the hydrolysis of fatty materials and from carbohydrate fermentation, are further broken down in an intermediate stage by enzymatic oxida- tion to form VFAs. Ultimately, the VFAs are further oxidized by bacteria to form carbon dioxide and water.

The specific objectives of this study were: (a) to compare the effects of bulking agents and amend- ments on the efficiency of the process; and (b) to demonstrate that the concentrations of ammonia and volatile fatty acid could be used as major indices of the effectiveness of the fish composting.

METHODS

Experimental facility The design of the composting facility has been reported previously (Holbek & Egan, 1992). A receiving tank, a mixing vessel, and four agitated, in- vessel composting bays which have dimensions of 50 m x 2.5 m x 1.25 m (length x width x height) are housed in a roofed structure. The system also includes a wastewater collection tank and an odour control system.

The composting mass in the composting bay is agitated and moved by a rotating drum. While turn- ing the composting material, the drum moves along a supporting track on the reactor walls. Short fingers on the outside of the rotating drum carry the com- post under the drum and also deposit it beyond the drum.

Materials The fish-waste material used in this research con- sisted for the most part of fish viscera. Alder chips and fir sawdust were tested as bulking agents, and peat moss and vermiculite as amendments. The fir mixture served as the control. Their pertinent chemical properties are presented in Table 1.

Table 1. Chemical parameters of bulking agents and fish waste

% TN % TOC C/N Moisture (dry weight) (dry weight) ratio content

<%) Fir 0.07 60.9 87.0 24 Alder 0.68 54.9 80.7 28 Peat 1.72 52.5 30.5 19 Vermiculite 0.02 0 0 1.0 Fish waste 9.23 63.3 6.86 68

The mixing ratios were calculated to achieve car- bon-to-nitrogen ratio (C/N) of 25/1 to 26/1. One part of fish waste and 1.3 parts of fir sawdust (by weight) were mixed to give a C/N ratio of 26/1. This mixture duplicates the current mixing practice of the facility (Liao et al., 1995). The calculated ratio for the alder mixture was two parts alder to one part fish waste (by weight) to give a C/N ratio of 25/1. For the mix made using peat moss as an amendment, peat moss, fir sawdust and fish waste constituted 15, 45 and 40%, respectively, of the total weight. The vermicu- lite mixture was made by adding 7% vermiculite to the normal mixing components of 1.3 parts fir saw- dust to 1 part fish waste.

Experimental design The experiments were conducted at the Vancouver Island facility. One composting bay was reserved for this particular study. Four different composting mixes were tested sequentially; these were the alder mix, the peat moss mix, the vermiculite mix and then the fir mix. The fir mix served as the control for the other treatments. Three runs of each mix were con- ducted. For each batch, the composting materials were retained in the composting bay for a period of 18 days. On days 1, 5, 9, 13 and 18, samples were collected for the purpose of chemical analysis. Each time, samples were taken from the depth of approxi- mately 20 cm below the surface of the composting mass. Samples were transported to the laboratory at the University of British Columbia for the necessary chemical tests, and for data analysis.

Analysis For each sample, moisture content, ash and pH were determined as described in Standard Methods (APHA, 1985). Ammonia and total Kjeldahl nitro- gen (TKN) were analyzed using a Technicon Autoanalyzer II. For TKN, a block digester was also required. The concentration of headspace ammonia was measured using Draeger tubes.

The presence of VFAs and phenol was deter- mined using a headspace gas chromatography (HS-GC) analysis technique. This technique involves sampling the headspace gas after equilibrium has been established between two-phases (gas-liquid or gas-solid) in a closed static equilibrated system. The quantification of compounds was determined by the external standard method. Values reported repre-

Composting offish wastes 165

sent the concentrations of the compounds in composts.

Chromatographic analysis was performed on a Hewlett-Packard (HP) 19395A automatic headspace sampler. This was attached to a HP 5890 gas chromatography equipped with a flame-ionization detector (FID). Volatile separation was accom- plished with a HP fused silica cross-linked FFAP column (0.53 mm I.D. x 1.0 #m film thickness × 30 m length). Gas chromatographic conditions were reported previously (Liao et al., 1994).

The mean and standard deviations were cal- culated for all parameters. The data were subjected to analysis of variance (ANOVA) and the least sig- nificant (LSP) test was used to separate means (e>0.05).

RESULTS AND DISCUSSION

Temperature Temperature profiles, presented in Fig. 1, display a similar pattern for all composting treatments. Tem- peratures increased rapidly to the thermophilic region (over 45°C) by day 5, and reached 55°C by day 10. In all runs, the maximum temperature achieved for each treatment was reached at the end of the monitoring period (day 18): the maximum achieved was approximately 70°C for the fir, alder and peat moss mixes, and 63°C for the vermiculite mix. In all runs, temperatures remained above 55°C for a period of 8 days, satisfying the regulatory requirement for the destruction of pathogens (USEPA, 1989). It should be noted that the upper level of the optimum range of the thermophiles involved in composting is between 55 and 60°C. At temperatures exceeding 60°C, the process becomes less efficient (Golueke, 1991). Except for the alder mix, temperatures were in this optimum range for

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Fig. 1. Temperature profiles of the composting mixes over time.

5-6 days (Fig. 1). Statistical analysis indicated that the temperature profile of the control was signifi- cantly different from that of the other mixes (e<0.005).

Moisture content According to Finstein et al. (1986), moisture loss during the composting process can be used as an index of the decomposition rate, since the heat generation which accompanies decomposition drives vaporization. In these experiments, however, no general trend was detected for the change in mois- ture content over the 18-day retention time, except that the alder mix showed a slight loss of moisture, as shown in Table 2. Other indices are therefore necessary for the progress of the composting pro- cess.

pH Figure 2 presents the results of monitoring the pH of the piles. When studying the effect of pH on composting, Jeris and Regan (1973) concluded that composting proceeds most efficiently at thermophilic temperatures when the pH is approximately 8. Ini- tially, the pH levels in this experiment indicated that all the piles were acidic and exceeded pH 8.0 on day I8 for all runs except the peat moss. Peat moss mix had consistently lower pH than the control, aider or vermiculite mixes (P< 0.005). The pH range in these experiments was therefore optimal for composting. The increase in the pH level during composting resulted from an increase in the volume of ammonia released due to protein degradation.

Table 2. Changes of total Kjeidahi nitrogen and moisture content in composts over time

Total Kjeldahl Moisture nitrogen, (%) TKN (8/1)

Fir Day 1 17.7+2.3 56.1 Day 5 17.1 +3.6 58.2 Day 9 16.3 +_ 1.2 57.8 Day 13 16.5 __+ 1.4 57.5 Day 18 14.3 +0.9 55.3

Alder Day 1 17.8 + 1.2 60.3 Day 5 16.2 + 1.3 59.4 Day 9 21.2 + 3.7 57.6 Day 13 23.7+4.0 56.5 Day 18 20.9 + 3.0 56.6

Peat moss Day 1 17.9+3.5 60.2 Day 5 20.6+3.4 61.3 Day 9 21.5 + 3.4 59.9 Day 13 17.6-t-6.9 61.6 Day 18 25.6-1-2.8 59.3

Vermiculite Day 1 13.8__+ 1.6 54.8 Day 5 20.8 +4.8 55.4 Day 9 20.4 -4-1.2 57.8 Day 13 22.1 __+ 1.4 56.1 Day 18 19.0 -4- 4.3 57.3

166

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P. H. Liao, L. Jones, A. K. Lau, S.

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Fig. 2. The pH of the composting mixes over time.

20

Ammonia and TKN in composting mixes The measured ammonia concentrations within the composting mixes are presented in Fig. 3. The over- all pattern which emerges from the ammonia results is that in all of the mixes, ammonia levels increased rapidly over the first 5 days of composting. During this period, the growing concentrations of ammonia in the composting piles appeared to coincide with greater microbial activity and therefore with more efficient composting. The rapid increase in ammonia levels also coincided with a rapid increase in tem- perature above ambient levels. Ammonia concentration reached the peak on day 5, when the temperature of all mixes was above 45°C, and then gradually declined. This pattern was similar to previ- ously reported results (Liao et al., 1995). In the previous study, ammonia levels increased in the first 3 days of composting, along with a rapid increase in

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temperature. Above 45°C, however, ammonia con- centrations no longer increased, but stayed at that level for a period of 6-9 days. When temperatures eventually exceeded 60°C, after 6-9days the ammonia concentrations started to decline. Because samples were taken more frequently than in this study, the relationship between ammonia concentra- tion and temperature was dearly demonstrated.

Ammonia-nitrogen levels in the fir compost mix had a significant difference from the composts con- taining alder or peat moss (P<0.01), the fir mix contained the most ammonia concentration of all the mixes. However, the contrast between the fir mix and the vermiculite mix was not different, this might be due to the fact that the vermiculite mix consisted of only 7% of vermiculite, with the balance made up of fish waste and fir sawdust. It should be noted that the fir mix had the most initial ammonia concentra- tion among all treatments; however, the loss of ammonia to the air was also the highest. On day 18, ammonia concentration in the fir mix was below the initial concentration, the other mixes were all above their initial concentrations.

TKN concentrations of the composting mixes are reported in Table 2. Initially, TKN concentrations for all mixes were very similar, except for the ver- miculite mix. Subsequently, TKN values on day 18 were lower (P<0"05) for the fir mix (14.3+0.9g/1) as compared to the other mixes (20.9+3"0 g/l for alder mix and 25.6 + 2.8 g/1 for peat moss mix).

Ammonia in the headspace The measured levels of ammonia gas in the head- space above the composting piles are shown in Fig. 4. The ammonia emissions are similar to the tem- perature profiles, with ammonia emissions from the control significantly higher than those from the

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Composting offish wastes 167

other treatments (P<0.005). In all cases, ammonia concentrations in the headspace increased continu- ally to day 18. The highest headspace ammonia concentration was observed in the fir mix, while the peat moss mix was the lowest. As the temperature of the compost piles increased, more ammonia was driven out. This was as expected, since the volatility of ammonia is known to be temperature dependent, and higher levels of ammonia above the composting pile should occur as the temperature of the com- posting pile increases.

As composting proceeded, the release of ammonia was further facilitated by increased pH of the compost piles (Fig. 2). The following formula demonstrates the relationship between ammonia and pH:

NH3 = [NH3 + NH ~ ]/(1 + [H + ]/Ka)

where NH3 is the ammonia concentration, N H : is the ammonium concentration, H ÷ is the hydrogen ion concentration, and Ka is the acid ionization con- stant of ammonia. At a higher pH, non-volatile ammonium ions are converted to the volatile ammonia form. Thus, as pH increases, more ammonia will be observed over the composting pile. The same figures show that less ammonia was lost to the air over the aider mix than over the fir sawdust mix. The availability of nitrogen in a form suitable for plants is an important criterion for a quality compost. In this regard, it is advantageous if ammonia is maintained in the compost and not lost to the ambient air as ammonia gas. This means that in terms of nitrogen management, alder makes a better bulking agent than fir sawdust. It should be noted that the loss of ammonia to the air was reduced by the additions of both peat moss and vermiculite, but peat moss was more effective than vermiculite in retaining ammonia. The reason is that peat moss contains acidic carboxyl and phenolic hydroxyl compounds, therefore, the peat moss mix had the lowest pH among the different treatments, except in the initial concentration (Fig. 2). As a result, more nitrogen was retained as ammonium in the peat moss mix and less ammonia was volatilized. Since peat moss is also an essential ingredient in potting mixes used for plant production, its use would probably be preferred. However, the results indicate that both peat moss and vermiculite could serve as useful amendments. The implication of this research is that nitrogen conservation in composts could be managed by the addition of a suitable amendment to the mix; it also implies that such amendments could serve as a useful method of odour control within the composting facility.

VFAs and phenol As stated in the introduction, VFAs are the inter- mediate products of biodegradation during

composting. It has been argued that an increase in these compounds should reflect the degree of micro- bial activity and the progress of decomposition. The results of the HS-GC analysis are reported in Table 2. Very high VFA concentrations were recorded for all mixes, indicating high levels of com- posting activity. The HS-GC analysis showed acetic, propionic, isobutyric, butyric, isovaleric and isoca- proic to be the major components. An overall trend is apparent: VFA concentrations increased rapidly in the beginning (first 5 days), remained constant until day 13 and decreased slightly towards the end of the active composting period. Figure 5, which uses acetic acid as an example, demonstrates this pattern. A similar pattern of changes in VFA concentrations occurring over time in fish composting was reported previously (Liao et al., 1995). These results therefore lend further support to the authors' contention that ammonia and VFA profiles can give a clear indica- tion of the progress of the fish composting process. In terms of acetic acid, the VFA concentrations for the alder mix were low compared to the control (P<0.1), this was probably due to a larger particle size of alder, but bears further investigation. No sig- nificant differences were found when compared to the peat or vermiculite mixes.

Phenol was also present in all composting mixes. It is likely that this chemical compound is produced as a microbial metabolite or as a product of lignin degradation and other aromatic substances in the composting mix. The concentration of phenol increased as composting proceeded, with the alder mix having the highest phenol concentration. This phenol concentration is higher than the others, as shown in Table 3 (P<0.005). If the phenol is pro- duced as suggested, this again points to alder as a better carbon source than fir sawdust.

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Fig. 5. Acetic acid concentrations in the composting mixes over time.

168 P. H. Liao, L. Jones, A. K. Lau, S. Walkemeyer, B. Egan, N. Holbek

Table 3. Changes of volatile fatty acids in composts over time (10 2 × mg/l)

Acetic Propionic Isobutyl Butyl Isovaleric Valeric Isocaprioc Caproic Capr ic Phenol acid acid acid acid acid acid acid acid acid

Fir mix Day 1 Day 5 Day 9 Day 13 Day 18

Alder mix Day 1 Day 5 Day 9 Day 13 Day 18

Peat moss mix Day 1 Day 5 Day 9 Day 13 Day 18

Vermiculite mix Day 1 Day 5 Day 9 Day 13 Day 18

22.4±6.2 14.5±4.6 9.21±3.3 19.9±5.2 18.3±6.4 0 2.43±0.8 0.15±0.30 0.54±0.65 0.45±0.34 29.6±9.6 22.1±2.9 ~.3±2.7 30.3_+5.4 29.2±4.7 0.54±1.1 3.89±1.1 0.80±1.59 0.42±0.49 0.~±0.24 36.6±4.7 25.8±2.3 22.0±1.7 35.7_+4.2 32.1±3.5 0.38±0.66 4.57±1.8 0.26±0.45 0.61±0.75 0.90±0.51 38.3±3.7 27.1±7.1 20.3±2.6 34.7±5.7 30.2±5.0 0.84±0.77 5.62±2.2 0.98±0.82 1.19±0.78 1.20±0.59 26.4±6.4 16.7±2.4 13.1±3.6 22.2±4.1 19.0±4.0 0 2.33±0.2 0 0.44±0.39 0.68±0.10

16.2±3.8 11.0±1.6 8.58±2.9 15.6±4.4 16.4_+4.6 0.55±0.67 4.02±2.2 0.82±0.76 1.29_+1.92 1.86±2.31 23.9±1.5 20.2±10.0 20.4±1.8 ~.4±9.3 28.7±11.2 1.23±0.62 9.63±3.3 0.77±0.35 1.41±0.~ 2.42±1.12 19.1±4.2 17.7±5.9 15.8±3.7 20.0_+2.5 25.1±5.9 1.34±0.~ 9.80±5.0 0.77±0.36 1.40±0.97 2.56±1.35 23.9±6.4 18.2±6.5 17.1±3.7 23.6±7.3 26.6±6.9 1.24±0.62 10.0±4.6 0.66±0.30 2.01±0.91 2.81±1.51 25.4±7.9 17.8±6.1 18.5±5.0 22.5±7.0 29.0±8.8 1.05_+0.53 9.30±4.3 0.76±0.55 2.66±1.20 3.13±1.56

16.4_+2.7 13.6±3.1 9.07_+1.4 19.7_+2.1 18.2_+2.7 0 2.71_+1.0 0 0.22±0.38 0.77_+0.12 32.7_+6.6 ~.2_+3.9 19.3_+4.3 31.4±5.5 33.5_+8.3 0 4.~±0.8 0.14_+0.28 0.59±0.54 1.01±0.27 34.0±8.6 28.2±9.6 21.8±6.2 36.7±12.5 36.5±12.1 0.54±0.80 4.21±2.7 0.71±0.92 0.~±0.45 0.85±0.19 28.2±11.1 18.7±12.4 15.0±7.7 24.9±13.5 25.2±14.1 0 3.16±1.5 0.19±0.33 0.56±0.49 0.86±0.36 26.4±7.3 15.6±6.1 13.9±3.4 22.0_+5.7 23.6±7.1 0 3.04±1.l 0 0.76_+0.1 0.99±0.27

21.2+4.1 13.2+2.7 9.28+2.8 20.0+3.5 17.5+4.4 0 2.39+0.12 0 0 0.77+0.44 33.7+6.9 21.2+4.9 18.9___+2.7 30.7+5.2 26.7+4.7 0 7.05+5.72 0.89__+1.30 1.38___+0.84 0.91+0.54 26.8+21.8 19.5+11.8 15.2+10.4 26.3-+19.7 23.3+17.1 0 6.37+7.47 0.27+0.46 1.21+1.83 1.05-+1.43 20.9+1.1 19.9+2.1 16.9+2. i 26.2-+5.5 25.8+5.1 0 7.05+6.94 0.51-+0.45 1.78+1.74 1.55-+1.72 28.5+8.1 21.1+6.8 16.8+4.4 25.7-+6.7 26.4+7.5 0.17_+0.41 3.48_+1.20 0 1.02+0.19 0.82_+0.22

CONCLUSIONS

The results of this research indicated that all mixes composted well. Ammonia emission from compost- ing piles were reduced by the addition of peat moss and vermiculite or using alder as a bulking agent. Ammonia management during the composting pro- cess could be easily accomplished by the use of suitable amendments or bulking agents. Peat moss and vermiculite were found to be good amendments and alder a good bulking agent. The changes of concentrations of headspace ammonia, ammonia- nitrogen and VFA in compost over time could serve as useful indices of the effectiveness and progress of the fish composting process.

A C K N O W L E D G E M E N T S

The authors gratefully acknowledge the financial support of the Science Council of British Columbia and the editorial services of Ms Jet Blake.

R E F E R E N C E S

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