anaerobic composting of crab-picking wastes for byproduct recovery

~,~l~i I ~'"'~ ~" ~ '? ELSEVIER P I I : S 0 9 6 0 - 8 5 2 4 ( 9 6 ) 0 0 1 0 4 - 6

Bioresource Technology 58 (1996) 265-272 Copyright © 1997 Elsevier Science Limited Printed in Great Britain. All rights reserved

0960-8524/96 $15.00

ANAEROBIC COMPOSTING OF CRAB-PICKING WASTES FOR BYPRODUCT RECOVERY

D. M. O'Keefe, a J. M. Owens b & D. P. Chynoweth b

"Full Circle Solutions, Inc., 2308 SE 41st Avenue, Gainesville, FL 32601, USA i, Bioprocess Engineering Research Laboratory, Agricultural Engineering Dept, University of Florida, Gainesville, FL 32611, USA

(Received 15 November 1994; revised version received 11 July 1996; accepted 30 July 1996)

Abstract The objective of this project was to determine the feasibility o f using two-stage anaerobic composting to stabilize crab-picking wastes, produce a residue amenable to byproduct recovery, and to compare flooded versus percolating operation o f the leachbed. Crab- picking waste (CPW) was treated using duplicate, two-phase reactor systems consisting of 14-1 leachbed reactors and 5-l hybrid sludge-bed filter reactors. Bio- chemical methane potential o f the CPW, solids reduction, methane production and leachate pH, alkalinity, conductivity, volatile organic acids (run 4 only), and chemical oxygen demand were monitored. Meth- ane yields approached or attained the BMP value (0.31 m 3 kg -I VS-O, except for run 2, which was stopped at 20 days due to mechanical problems. Mean solids reduction was 80% (SD = 2). Residues were not odoriferous, had a low bulk density (85g l - t ) and were stored at ambient temperature with no vector attraction potential There was no difference in methane yield or VS conversion between percolating and flooded operation o f the leachbeds. Copyright © 1997 Elsevier Science Ltd.

Key words: Anaerobic composting, two-stage digestion, methane, chitin, food-processing waste.

INTRODUCTION

Disposal of solid waste generated by crab-processing facilities is a significant problem, partially due to its highly putrescible nature, allure to insects and pests, and odor-producing potential (Brown, 1981; Aver- bach, 1981; Boardman et al., 1987; Verscharen, 1989). Available alternatives for disposing of this waste include crab-meal production, ocean dumping, landfilling, aerobic composting (Averbach, 1981; Cathcart et al., 1986; Cato, 1992) and anaerobic composting (Andree et al., 1992). The use of crab meal in animal feeds is often not economical due to the supply and low cost of proteins from soybean production (Brown, 1981). Ocean dumping has the potential to cause environmental damage to fragile

265

estuary ecosystems by lowering productivity due to increased turbidity and depressed dissolved oxygen levels, and by promoting microbial contamination of shellfish beds (Boardman et al., 1987). Landfilling of this waste is no longer acceptable due to increased landfill costs and, in Florida, recent solid waste legis- lation (Averbach, 1981).

Technical feasibility of aerobic composting of crab-picking waste (CPW) has recently been demonstrated both in the lab and at field scale (Cathcart et al., 1986; Brinton & Gregory, 1992). The moisture and nitrogen content of CPW is significantly higher than levels recommended for optimal compost feed- stocks, so the use of significant amounts of bulking agents are required (Merkel, 1981; Brinton & Greg- ory, 1992). With optimal conditions the initial stabilization of this waste can occur within 21 days using a relatively low cost windrow composting system (Brinton & Gregory, 1992).

Aerobic windrow composting of this waste suffers from a number of potential drawbacks owing to the nature of CPW. First, odor control will depend on meticulous and immediate incorporation of CPW with the required bulking agent followed by covering the pile with finished compost. Any delay in processing this waste will increase odor emissions and fly breeding potential. In addition, the rapid initial rates of oxygen consumption and heat production within the pile necessitate frequent aeration to prevent the onset of microbial imbalance with concomitant odor production. Another factor is the potential for groundwater and surface-water contamination due to leachate production during periods of high pre- cipitation. The biological oxygen demand (BOD) of CPW leachates can reach 300000 mg 1 -~, which is 1000 times greater than typical municipal wastewater (Verscharen, 1989). Also, the incorporation of bulking agent results in no net volume reduction of the initial CPW volume. Finally, the potential end-use of finished CPW compost is limited to use as a soil- conditioner, potting soil or landfill cover, all relatively low-value uses.

266 D. M. O'Keefe, J. M. Owens, D. P. Chynoweth

The shells of the blue crab contain compounds of potential commercial value. In aerobic composting, the incorporation of the crab shell into the bulking agent prevents simple recovery of the shell from the finished compost, limiting the potential for byproduct recovery. Pigments found in crab shells, such as astaxanthin (Manu-Tawiah & Haard, 1992), can be used in the manufacturing of surimi to improve appearance. The use of these pigments in aquaculture feed mixtures can improve the appearance of tropical fish, as well as farm-raised trout (Manu-Tawiah & Haard, 1992). Chitin, another significant component of crab shells, is currently marketed as a slow-release organic fertilizer and is reported to have nematocidai properties (Godoy & Morgan-Jones, 1983; Mian et al., 1982). Crab shells have been shown to have an affinity for adsorbing certain heavy metals and may have significant value in water-treatment applications (Boardman et al., 1987). Finally, chitin can be used as an industrial raw material for chitosan production, which has several potential commercial uses, including as a coagulant, as a main ingredient in film and fiber polymer production and as a chelating agent (Aver- bach, 1981).

As an alternative to CPW disposal by aerobic composting, anaerobic composting offers several advantages, particularly where the former is defi- cient. Since all liquids, solids, and gases are contained or captured in the anaerobic process there is less potential for odors and environmental damage. Reactor vessels are sealed and pests do not have ready access to the waste solids. Since there is no requirement for aeration the use of bulking agents for moisture reduction is not necessary, allowing for substantial volume reduction. In addition, the anaerobic process produces a useful biogas fuel, which may be used at the crab-processing plant. Lastly, the residue from anaerobic composting of CPW will be enriched with shell material, facilitating byproduct recovery.

The proposed approach to treatment of crusta- cean waste may make the establishment of chitosan/chitin extraction facilities in the U.S. economically feasible. One reason that chitosan/chitin extraction facilities are currently not economically feasible in the U.S. is that shell production is too spread out, production facilities are too small and the shell needs to be transported immediately due to its putrescible nature. Averbach (1981) believes that for a chitosan/chitin facility to be profitable all raw materials need to be with a 50-mile radius of the plant. If shell could be converted into a stable, dry product at the processing facility, the material could be stored in trailers or containers until sufficient quantities had accumulated to warrant the cost of shipping. This would expand the region that could economically supply a chitosan/chitin extraction facility considerably beyond 50 miles.

Andree et al. (1992) reported successful anaerobic stabilization of blue crab scrap using a one-phase reactor system. They achieved a methane yield of 0.22 m 3 kg-~ VS in 65 days. Frequent removal and storage of leachate and addition of water was required to dilute the leachate to avoid 'pickling'. While this work demonstrated the feasibility of anaerobically digesting the crab waste, using this procedure would be impractical at full-scale.

Preliminary attempts at anaerobic composting of CPW in a single-phase high-solids batch reactor resulted in a rapid increase in soluble chemical oxygen demand (COD) to 86000 mg 1 -~, insignificant gas production and a 'pickling' of the reactor con- tents (O'Keefe, unpublished data). As mentioned above, Andree et al. (1992) addressed this problem by removing leachate, diluting the remaining leachate, and storing the extra leachate for later treatment. These preliminary results demonstrate the rapid kinetics for acid formation in CPW and suggest the need for a methane phase capable of rapid assimilation of soluble products. The upflow anaerobic sludge-blanket (UASB) reactor (Lettinga et al., 1984), modified with the addition of a fixed- media filter above the granual sludge, meets these requirements and was incorporated into our proposed methane-phase reactor design for anaerobic treatment of crab-processing wastes.

In two-phase anaerobic biodegradation of organic matter the first phase involves solubilization, depoly- merization and conversion of organic matter into fermentation products and, in the second phase (the anaerobic digester), the soluble matter is converted to methane and carbon dioxide. However, experi- ments with this concept typically result in rapid inoculation of the first phase and its subsequent conversion to a methane-producing combined-phase system (Rijkens, 1981). Some of the potential advantages of two-phase over combined-phase treatment are: (1) since the two phases have different growth rates and optima for environmental and nutrient conditions, phase separation should result in improved performance; (2) phase separation pro- vides the opportunity to establish pH and pressure swings needed for methane enrichment of the resulting biogas through enhanced stripping of CO2 in the first phase; and (3) phase-separation results in improved process stability through maintenance in the methane phase of active populations of bacteria that can utilize volatile organic acids (VOA) which, if not metabolized, can result in process imbalance (ensiling). Because of these advantages, two-phase treatment is reportedly more rapid and more stable than combined-phase treatment (Cohen, 1983; Ghosh & Klass, 1978; Massey & Pholand, 1978; Zoetemeyer et al., 1982). In this investigation the authors were primarily interested in the third advan- tage and anticipated that the HSFB reactor would produce methane as quickly as possible.

Byproduct recovery from crab-picking wastes" 267

In two-phase anaerobic composting of CPW, the crab proteins and viscera are expected to rapidly ferment and leach from the leachbed into the aqueous phase, which can be drained and pumped into a high-rate anaerobic leachate digester where these odorous compounds are rapidly converted to methane and carbon dioxide. The treated liquid may be returned to the leachbed reactor to percolate through the solids and entrain more fermentation products. After rapid stabilization the final residue is expected to contain mostly shell material with little odor-producing potential.

The objective of this research was to demonstrate the feasibility of using two-stage anaerobic composting to stabilize crab-picking wastes and to produce a residue which is amenable to economic byproduct recovery and to compare flooded versus percolating operation of the leachbed.

M E T H O D S

Fresh crab-picking waste was obtained from Gulf Stream Crab Company, a crab-processing plant in Steinhatchee, Florida. The waste was brought to the University of Florida in Gainesville and kept frozen until used. The waste consisted of the boiled remains of blue crabs (Callinectes sapidus). Remains included the shells, viscera and remaining crab meat. Total and volatile solids analyses were performed on the fresh waste and all residues from the biochemical methane potential (BMP) assay and reactor runs according to Standard Methods (Clesceri et al., 1989). Table 1 summarizes the results from the solid analyses of the untreated crab-picking waste and the solid residues.

Statistical comparisons of methane yield, solids conversion, and leachate characteristics between percolating and flooded operation of the ieachbeds were done using analysis of variance.

Biochemical methane potential (BMP) of blue-crab waste Prior to treating crab waste in bench-scale anaerobic digesters, the biochemical methane potential (BMP) of the waste was determined following the methods described by Owen et al. (1979). Approximately 1 l of the raw waste was blended for 1 min. Three 0.2 g

volatile solid (VS) subsamples of the blended waste were used in the BMP assay.

Triplicate bottles were assayed for biochemical methane potential (BMP) using a sample concentration close to 2 g VS l-J. Media containing nutrients and trace metals were prepared according to this method, except for trace amounts of additional minerals (0.19mg 1 -I HzWO4 and 4.05mg 1 -~ NiCI2.6H20) and a 20% (v/v) inoculum. Inoculum was taken from a 5-1, mesophilic (35°C), continuously stirred digester (CSTR) intermittently fed 1.6 g VS 1-1 day-~ at a hydraulic retention time of 20 days. Primary sludge obtained from the City of Gainesville municipal sewage treatment plant served as feed for the CSTR.

In serum bottles (275 ml nominal volume), 100 ml of inoculated medium was added to the sample in an atmosphere of nitrogen. Sealed bottles were inverted and incubated at 35°C. Each assay was accompanied with positive controls of Avicel cellulose (FMC Cor- poration) and blank controls containing only inoculated medium.

Assay bottles were periodically analyzed for gas production and composition. A gas-tight syringe fitted with a No. 23 needle was inserted through the septum and allowed to equilibrate to barometric pressure. The gas was injected into a GC column of Porapak Q and eluted into a thermal conductivity detector. The method was calibrated using an external standard gas containing CH4, CO2, N2 and O2.

After each sampling, the value of the measured volume of methane produced by the bottles was converted to dry gas at 1 atm and 0°C (STP) and added to the previous measurements. This cumulative methane volume removed was added to the methane (dry at STP) present in the headspace of the bottle to determine the total cumulative methane volume at the sampling time. The total cumulative methane volumes were corrected for methane production attributed to the medium and inoculum by subtract- ing the averaged blank control volumes from each bottle's total cumulative methane volume. Finally, the corrected cumulative methane yield was cal- culated by dividing the corrected volume by the weight of sample VS added to each bottle.

The degradation of each sample was assumed to follow a first-order rate of decay. Thus, the production of methane was assumed to follow:

Table 1. Total solids (TS) and volatile solids (VS) for untreated crab-picking waste and the solid residue resulting from anaerobic composting and drying under ambient conditions

Crab-picking waste Final solid residue

TS (%) VS (%) TS (%) VS (%)

Mean 31 69 97.25 34.5 Standard deviation 2.78 1.19 1.79 4.77


t "

)0 t < hag y= Y~(1-e -ku-t'a,)) t>~hag

where Y is the cumulative methane yield at time t, Y~, is the ultimate methane yield, k is the first order rate constant, hag is the lag time. The parameters, Y ~ , k and hag were estimated using a nonlinear regression fit to the yield data of a triplicate set. The regression was performed on a PC-compatible com- puter using the Marquardt-Levenberg algorithm available in SigmaPlot 4.0 (Jandel Scientific, 1989).

Reactor des ign and operat ion Crab-picking waste was treated using duplicate, two- phase reactor systems (Fig. 1). Each reactor system consisted of a 14-1 leachbed reactor and a 5-1 hybrid sludge-bed filter (HSBF) reactor. The leachbeds were constructed of 20-cm (ID) PVC tubes with plexiglass tops and bottoms attached to the tube with flanges. The HSBF reactors were constructed of 15-cm (ID) steel pipe. Filters were fabricated from 5-cm thick discs of fiberglass air filter material cut to fit the inside diameter of the vessel and placed immediately below the leachate outflow port in the HSBF.

The leachate circulation system consisted of 8-mm (ID) Tygon tubing and one peristaltic pump (Cole-Parmer) with four heads. Four valves controlled flow direction allowing for leachate circulation between or within vessels. Temperature was monitored and controlled using J-type thermo- couples, heating strips and temperature controllers.

The leachbeds were operated at ambient tem- peratures (approximately 2 0 ° C ) a n d the HSBF reactors at 35°C. Leachate was continuously circu- lated between the reactors. Hydraulic retention time of the HSBF was approximately 2 h. Leachate was initially obtained from pilot-scale, thermophilic municipal solid waste digesters, Leachate lost

though evaporation, sampling, or removal with spent CPW was replaced with distilled water. A leachate volume of approximately 4000 ml was maintained in the HSBF reactor vessels. Leachate volume in the leachbed was 4000 ml for runs 1 and 2 (percolating operation) and 10.5 1 for runs 3 and 4 (flooded operation). Sludge granules for the HSBF were obtained from a mesophilic reactor treating ethanol distillery waste. The volume of the sludge used was 2000 cm 3 per HSBF reactor.

Gas analysis Gas volume produced by the HSBFs during all runs, and the leachbeds during runs 4 and 5 was monitored using a manometer-type gas meter developed at the University of Florida. A gas inlet and outlet were located on one end of a clear PVC U-tube and a float switch was on the other end. As gas entered, liquid was displaced, causing the float switch on the other side of the U-tube to activate a solenoid which shut off the incoming gas and vented gas from the U-tube. The water level in the tube became equal- ized again. A counter connected to the switch recorded the number of cycles. The amount of liquid in the tube and the float switch was adjusted to give 50 ml of gas per cycle. Gas volume produced by the leachbed during runs 1 and 2 was measured using a water-displacement meter filled with H2SOa-acidi- fled water.

Gas composition (02, CO2, CH4 and N2) was determined using a gas chromatograph equipped with two matched pairs of thermal conductivity detectors and dual stainless-steel columns operated at 55°C. The first column was 2 m x 3.2 mm packed with 80-100 mesh Porapak Q (Supeico, Inc.) and the second column was 3.35 m x 4,8 mm packed with 60-80 mesh molecular sieve 13X (Supelco, Inc.). Helium was the carrier gas at a flow of 30 cm 3 min- t.

Leachate Level Runs 3,4

Crab Waste--

Perforated Plate ~x~

Leachate Level Runs 1,2

Headspace Connection

• ,....:..:: ,...- .. . . " . . -

. _ - _ ~ . _ _ _ _ - . . . . . . - . . . .

-_~ _ - _ - _ _ - - _ - . . . . _ - _ .

-~ - - ---- Pump

. . . . - - - . . . . z . . . . z~

• 1 - - - (4)

'

Pump

Tc Gas Meters

iiiiiiii!iiiiii iii ii!!i iii i

Leachate Level

Filter

Granular Sludge

Leachbed Hybrid Sludge-Bed Fi l ter (HSBF)

Fig. 1. Schematic of two-phase anaerobic digestion system used to treat blue-crab-picking wastes.

Byproduct recovery from crab-picking wastes 269

Leachate analysis Throughout all runs leachate leaving all reactor vessels was analyzed for pH, soluble chemical oxygen demand (COD), alkalinity, electrical conductivity (EC) and solids according to Standard Methods (Clesceri et aL, 1989). Volatile organic acids (VOA) were determined throughout run 4 using flame-ionization gas chromatography. The VOA concentration was determined by acidifying samples with the addition of 20% (v/v) H3PO4 to a final concentration of 2% (v/v). Samples were then centri- fuged and 1/~1 of the supernatant injected onto a 1.8 m x2.0 mm glass column of 10% SP-1000 on 100/120 Chromosorb W/AW (Supelco, Inc). The column was maintained at 140°C with nitrogen as the carrier gas at 40 cm 3 min- t. The injector was set at 160°C and the flame-ionization detector to 200°C. The total VOA concentration reported here repre-

>~

t f ]

(.9

7

E~ C) ~Q

0.4

~c~

0 ~

0 .2

0.1

0 . 0

] r T 1 T I I I

~/,(3/ •

• . . . . . . . . . •

l ' O

- 0 C e l l u l o s e C o n t r o l (CO)

• C r a b P i c k i n g W a s t e (CPW)

CC CPW 3 1

l t i m a t e Y i e l d = 0 . 3 9 0 .31 m k g -1

: a t e C o n s t a n t = 0 . 1 0 0 . 1 0 d

I I I I I I

0 20 30 4 0 5 0 60 7 0 8 0 90

TIME (days) Fig. 2. Cumulative methane yield (methane reported at STP, 1 atm, 0°C) of crab-picking waste and cellulose control in standard 100ml biochemical methane potential

assays incubated at 35°C.

sents the sum of acetic, propionic, iso-butyric, n-butyric, iso-valeric and n-valeric acids.

RESULTS AND DISCUSSION

Biochemical methane potential (BMP) of blue-crab waste Figure 2 illustrates the cumulative methane yield of CPW (0.31 m 3 kg -~) in comparison to a cellulose control (CC). While the ultimate yield is lower for the CPW than the CC, ultimate methane yields greater than 0.2 m 3 kg -~ are considered favorable for any feedstock. The first-order rate constant for both CPW and CC is 0.1 day--1, which indicates more than 86% of the degradation occurs in the first 20 days. The residue that remains consists of shell material that is not readily anaerobically degradable without chemical pretreatment (Lee, 1992). The relative recalcitrance of the shell material compared to the readily putrescible meat and fat fractions is a fortunate circumstance that allows for the recovery of this potentially valuable byproduct.

Gas production and solids reduction Methane yields approached or attained the BMP value in all reactor runs except for run 2, which was stopped at 20 days due to mechanical problems (Table 2) Mean solids reduction for all runs was 80% (SD = 2) with an average of 54% (excluding run 2) of the reduced solids accounted for by the total biogas production. This suggests that some component of the ash, perhaps CaCO3, was being dissolved during digestion. When sun-dried for a few hours, spent residues were not odoriferous, had a low bulk density (85 g 1000 cm -3, 5 lbs ft-3), and could be stored at ambient temperature with no vector attraction potential. Methane production rates typically increased for the first 2 weeks and then dropped off quickly (Fig. 3) suggesting that crab- waste VS is quickly solubilized and readily leachable. There was no difference (P>0.05) in methane yields

Table 2. Volatile-solids (VS) and methane-yield results for four duplicated, two-phase digester runs. The digesters were loaded with blue-crab-processing waste

Run Run length, Starting Final Methane Volatile Volatile days volatile volatile yield, solids solids

solids, solids, 1 CH4 g- ~ VS reduction, recovered as g g % biogas,

%

Percolating operation 1

Flooded operation 3

47 Mean 331 71 0.246 78 64 SD" 22 7 0.041 4 2

20 Mean 336 61 0.098 82 24 SD 0 19 0.012 6 2

28 Mean 290 62 0.312 79 50 SD 0 10 0.074 3 9

28 Mean 290 56 0.274 81 49 SD 0 3 0.003 1 1

"Standard deviation.

270 D. M. O'Keefe, 7, M. Owens, D. P. Chynoweth

or VS reduction between runs employing percolating or flooded operation (Table 2). The average methane content of the gas was 61% for the leachbed and 65% for the HSFB. After the first 3 weeks of a run the methane content of the gas was often above 70%, due to the high protein content of the waste.

Leachate characteristics Leachate characteristics are summarized in Table 3. Crab-waste leachate was strong, even during the

runs where the leachbed was flooded. However, no dilution was required to achieve process stability. Except for COD levels, leachate characteristics were similar between the leachbeds and HSBFs. Alkalin- ity tended to increase during a run, while pH and electrical conductivity (EC) remained relatively constant (Fig. 3). Chemical oxygen demand (Fig. 3) and volatile organic acids (VOA) during run 4 (Fig. 4) increased during the first 2 weeks and then rapidly dropped off. There were significant differences

=T

0 0 0

~ 4

~ 3

• HSBF [ Right Axis] Left Axis

o" o o

I I I 12000

11000

10000

• • , • '9ooo

~ 8000

I 7000

6000

d~

0 c,~

t ' - I

8.0

7.8

7.6

7.4

7.2

7.0

,,0 • o

I I i

0 0

0

0 0

# ° 8,

I I

0 O,@ I

15000

12000

9000

6000

3000

0 r0

I

0 ~4

d)

©

0

0

I:Z.,

1000

90O

80O

70O

600

50O

400

500

200

100

0

I I

I I I

7 14 21

Time (d) S y s t e m 1

I I I 0.5

0.4

0.3

.2

0.1

0.0 280 7 14 21 28

Time (d) S y s t em 2

,.<

t "

0~ I

O~

Fig. 3. Chronological summary of leachate characteristics and methane production of duplicate two-phase reactor runs (run 4) treating blue-crab-picking wastes.

Byproduct recovery from crab-picking wastes 271

Table 3. Summary of leachate characteristics of four duplicated two-phase anaerobic digester runs treating crab-picking wastes

Average elecrical Average pH Average alkalinity, Final COD, conductivity, mg CaC03 1 -~ mg 0 2 l- mohms cm- J

Leachbed HSBF Leachbed HSBF Leachbed HSBF Leachbed HSBF

Percolating Mean 8.7 8.1 7.6 7.5 9929 10321 7576 7402 Min. 0.7 0.7 6.7 6.3 6167 7750 2404 2115 Max. 14.3 14.5 8.3 7.8 12667 12625 21 924 29256

Flooded Mean 3.3 3.3 7.7 7.7 7185 7399 1990 1939 Min. 2.3 2.8 7.4 7.4 1667 3833 1899 1916 Max. 4.2 4.4 7.9 7.9 9583 9500 6371 5810

ANOVA P value <0.0001" 0 .0001" 0 . 2 0 1 0 0 . 3 2 0 7 0 . 1 0 5 6 0 . 0 9 7 2 0 .0124" 0.0023* Standard error 0.28 0.34 0.07 0,17 1018 1052 1120 760

"Denotes significant difference between the flooded and nonflooded runs at the 95% confidence level.

(P_<0.05) between the percolating and flooded runs for EC and final COD but not pH and alkalinity. These differences are dilution effects and did not have any effect on process performance. It was originally thought that flooded operation would

2 5 0 0 ~ r f

o h e a c h b e d 2 2 5 0

• HSBF

,~oo ~ Sys t em #1 l 1 7 5 0 K / ' - - \ \

1 5 0 0 \

• \

0 1

• ~ f,, /

o L e a e h b e

~,-~ ' \ • HSBF | ? , q ) o l / '

~ / Sys t em #2 [ 750 / " / /

1:5(3 [ ,~

f/ 4

. 5 0 i

!) , . . . . . . . 1 ~ I I

I 7 1 4 2 1 2 8

Time (d) Fig. 4. Volatile organic acid concentrations in the leachate from the leachbed and HSBF during run 4 for systems 1

and 2.

move soluble products out of the leachbed more rapidly and therefore improve process performance, but this was not the case. The fact that dilution of the leachate did not improve process performance, coupled with the stability of the two-phase process, suggests that for full-scale facilites two-phase systems would be superior to one-phase systems. The high strength of the waste in the one-phase systems requires dilution and therefore larger reactor vessels, or removal of leachate from the reactor vessel.

C O N C L U S I O N S

Crab-picking waste proved readily treatable using a two-phase anaerobic composting system. The reactors were very stable, despite the high soluble COD of the waste. The waste has a high methane potential and the resulting biogas has a high methane content, thus reducing requirements for gas clean- up. There was no difference in reactor performance (methane yield or VS conversion) between the percolating and flooded modes of operation. The residue is an odorless, low bulk density material that could be stored and shipped with few limitations. The residue is useful as a raw material for chitin extraction, organic fertilizer, or liming agent.

R E F E R E N C E S

Andree, S. W., Earle, J. F. & Lee, H. (1992). In-plant methods for handling blue crab scrap. In Compos#ng and Using By-products from Blue Crab and Calico Scal- lop Processing Plants in Florida, ed. J. C. Cato. Florida Sea Grant, Gainesville, Florida, pp. 6-12.

Averbach, B. L. (1981). Chitin-chitosan production for utilization of shellfish wastes. In Seafood Waste Manage- ment in the 1980s: Conference Proceedings, 23-25 September 1980, Orlando, Florida, ed. W. S. Otwell. Report No. 40, Florida Sea Grant College.

Boardman, G. D, Flick, G. J. & Kramer, T. A. (1987). Effects of crab scraps on marine environments. In Proc.


Food Processing Waste Conf., 1-2 Sept 1987, Georgia Institute of Technology, Atlanta, Georgia.

Brinton, W. F. & Gregory, H. C. (1992). Composting of Florida blue crab scrap. In Composting and Using By- products from Blue Crab and Calico Scallop Processing Plants in Florida, ed. J. C. Cato. Florida Sea Grant, Gainesville, Florida, pp. 13-30.

Brown, Kimball, F. (1981). Crab meal production: tragic impact on the blue crab industry unless viable alternatives established. In Seafood Waste Management in the 1980s: Conference Proceedings, 23-25 September 1980, Orlando, Florida, ed. W. S. Otwell. Report No. 40, Flor- ida Sea Grant College.

Cathcart, T. P., Wheaton, F, W. & Brinsfield, R. B. (1986). Optimizing variables affecting composting of blue crab scrap. Agric. Wastes, 15, 269-287.

Cato, J. C. (1992). Composting and Using By-products from Blue Crab and Calico Scallop Processing Plants in Flor- ida. Florida Sea Grant, Gainesville, Florida.

Cohen, A. (1983). Two-phase digestion of liquid solid wastes. Third Int. Syrup. on Anaerobic Digestion Pro- ceedings, 14-19 August 1 9 8 3 , Cambridge, Massachusetts, USA, pp. 123-138.

Clesceri, L. S., Greenberg, A. E. & Trussell, R. R. (1989). Standard Methods for the Examination of Water and Wastewater, Edition 17. American Public Health Associ- ation, Washington, DC.

Ghosh, S. & Klass, D. L. (1978). Two-phase anaerobic digestion. Proc. Biochem., April, 15-24.

Godoy, G. R. & Morgan-Jones, G. (1983). Chitin amendments for control of Meloidogyne arenaria in infested soil. II. Effects on microbial populations. Nematropica, 13, 63-74.

Jandel Scientific (1989). SigrnaPlot Scientific Graphing Software Version 4.0 Users Manual. Jandel Scientific, Corte Mader, California.

Lee, H. (1992). Ultimate methane yield of pretreated blue crab waste. Masters degree thesis, University of Florida, Gainesville, Florida.

Lettinga, G., Hulshoff Pol, L. W., Koster, I. W., Wiegant, W. M., De Zeeuw, W. J., Rinzema, A. , Grin, P. C., Roersma, R. E. & Hobma, S. W. (1984). High-rate anaerobic waste-water treatment using the UASB reactor under a wide range of temperature conditions. In Biotechnology and Genetic Engineering Review, Vol. 2, ed. G. E. Russell. Intercept Ltd, Newcastle Upon Tyne, UK, pp. 253-284.

Massey, M. L. & Pholand, G. G. (1978). Phase separation of anaerobic stabilization by kinetic controls. J. Water Pollut. Control Fed., 50, 2204-2222.

Mian, I. H., Godoy, G., Shelby, R. A., Rodriguez-Kabana, R. & Morgan-Jones, G. (1982). Chitin amendments for control of Meloidogyne arenaria infested soil. Nematro- pica, 12, 71-84.

Manu-Tawiah, W. & Haard, N. F. (1992). Recovery of carotenoprotein from the exoskeleton of snow crab Chionocetes opilio. Can. Inst. Food Sci. Technol. J., 20(1), 31-33.

Merkel, J. A. (1981). Managing Livestock Wastes. AVI, Westport, Connecticut.

Owen, W. F., Stuckey, D. C., Healy, J. B. Jr., Young, L. Y. & McCarty, P. C. (1979). Bioassay for monitoring biochemical methane potential and anaerobic toxicity. Water Res., 13, 485-492.

Rijkens, B. A. (1981). A novel two-step process for the anaerobic digestion of solid wastes. In Energy from Bio- mass and Wastes. Institute of Gas Technology, Chicago, pp. 463-475.

Verscharen, J. A. (1989). An analysis of seafood processing wastewater and potential pretreatment methodology for small seafood processors. In 1989 Food Processing Waste Conf., 6-8 November 1989, Georgia Institute of Technology, Atlanta, Georgia.

Zoetemeyer, R. J., Arnoldy, P., Cohen, A. & Boelhouwer, C. (1982). Influence of temperature on the anaerobic acidification of glucose in a mixed culture forming part of a two-stage digestion process. Water Res., 16, 313-321.

anaerobic composting of crab-picking wastes for byproduct recovery

Documents