Anaerobic digestion of stillage from a pilot scale wood‐to‐ethanol process II. Laboratory‐scale digestion studies

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<ul><li><p>This article was downloaded by: [Dalhousie University]On: 04 October 2014, At: 23:59Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK</p><p>Environmental Technology LettersPublication details, including instructions for authors and subscription information:</p><p>Anaerobic digestion of stillage from a pilot scalewoodtoethanol process II. Laboratoryscale digestionstudiesI.J. Callander (deceased) a , T.A. Clark a &amp; P.N. McFarlane aa Biotechnology Section, Wood Technology Division , Forest Research Institute , Private Bag,Rotorua, New ZealandPublished online: 17 Dec 2008.</p><p>To cite this article: I.J. Callander (deceased) , T.A. Clark &amp; P.N. McFarlane (1986) Anaerobic digestion of stillage from a pilotscale woodtoethanol process II. Laboratoryscale digestion studies, Environmental Technology Letters, 7:1-12, 397-412, DOI:10.1080/09593338609384427</p><p>To link to this article:</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (the Content) contained in thepublications on our platform. However, Taylor &amp; Francis, our agents, and our licensors make no representationsor warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Anyopinions and views expressed in this publication are the opinions and views of the authors, and are not theviews of or endorsed by Taylor &amp; Francis. The accuracy of the Content should not be relied upon and should beindependently verified with primary sources of information. Taylor and Francis shall not be liable for any losses,actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoevercaused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.</p><p>This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms &amp; Conditions of access and use can be found at</p><p></p></li><li><p>Environmental Technology Letters, Vol. 7, pp. 397-412 Science &amp; Technology Letters, 1986</p><p>ANAEROBIC DIGESTION OF STILLAGE FROMA PILOT SCALE WOOD-TO-ETHANOL</p><p>PROCESSII. LABORATORY-SCALE DIGESTION STUDIES</p><p>I.J. Callander (deceased), T.A. Clark*, and P.N. McFarlaneBiotechnology Section, Wood Technology Division,</p><p>Forest Research Institute, Private Bag, Rotorua, New Zealand</p><p>(Received 23 June 1986; accepted 3 July 1986)</p><p>ABSTRACT</p><p>The anaerobic digestion of stillage from a pilot-scale wood-to-ethanol processwas investigated using an 8-litre, continuously-fed reactor. A methanogenicconsortium acclimated to Pinus radiata stillage was developed over 160 days bymaintaining a low organic loading rate. The loading rate was then graduallyincreased to c. 4 kg COD m-3 day-1. Nutrient, alkalinity, and mineralrequirements were quantified. Approximately 90% COD removal was obtained atspecific COD utilisation rates up to 0.5 g COD g VSS~1 day-1. The methane andtrue cell yields, per gram of soluble COD removed, were 0.313 1 CH4(STP) and0.142 g VSS. The endogenous decay coefficient was 0.0083 day-1.</p><p>INTRODUCTION</p><p>Part one (1) of this two part paper described the characteristics of awood-ethanol stillage, i.e., the wastewater produced by the New Zealand ForestResearch Institute (FRI) pilot-plant process of the conversion of Pinus radiatawood to ethanol. Anaerobic digestion was selected as a suitable stillage-treatment process for study because it displayed more favourable economics thanaerobic, wet oxidation, and evaporation treatment processes (2) and because it hasbeen successfully applied to the treatment of a variety of stillages (3-14). ofthe previous studies only Good et al (3) investigated the treatment ofwood-ethanol stillage. This effluent was generated from a large demonstration-scale plant using dilute sulphuric acid hydrolysis of eucalypt wood (3), a processsimilar to that used by the FSI pilot plant. Anaerobic digestion was a suitabletreatment for this stillage which was similar in composition to the P. radiatastillage produced by the FRI pilot plant (Table 1), even though it was derivedfrom a hardwood rather than a softwood. Because of the difference in stillageorigin, the compositions of potentially toxic, lignin-derived compounds in theP. radiata stillage could be expected to differ significantly from those ofcompounds in the eucalypt stillage.</p><p>This paper describes initial laboratory studies on the anaerobic digestion ofPinus radiata wood-ethanol stillage from the FRI dilute acid hydrolysis pilotplant. The study's aims were (1) to develop an anaerobic biomass acclimated to</p><p>397</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Dal</p><p>hous</p><p>ie U</p><p>nive</p><p>rsity</p><p>] at</p><p> 23:</p><p>59 0</p><p>4 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>P. radiata stillage; (2) to quantify its nutrient, mineral, and alkalinityrequirements, and then (3), to assess the efficiency of the digestion processunder conditions of increasing organic loading rate.</p><p>TABLE 1 - Comparison of the characteristics of the wood-ethanol stillagereported by Good et al (3) and that used in the present study</p><p>Parameter(g i-l except pH)</p><p>Eucalyptstillage</p><p>Good et al (3)</p><p>P. radiatastillage (1)</p><p>Chemical Oxygen Demand (COD)</p><p>Total Solids (TSS)</p><p>Volatile Solids (VSS)</p><p>Ash</p><p>S total</p><p>N total</p><p>P total</p><p>pH</p><p>COD:N:P</p><p>22.5</p><p>17.6</p><p>15.6</p><p>2.0</p><p>0.26-0.36+</p><p>0.2+</p><p>.0.04 +</p><p>5.8-6.3</p><p>100:0.88:0.17</p><p>25.5</p><p>13.7</p><p>8.8</p><p>4.9</p><p>0.60</p><p>0.095</p><p>0.010</p><p>4.5-5.0</p><p>100:0.37:0.04</p><p>Nitrogen and phosphorus have been added to the eucalypt stillage, and its levelof sulphur has been adjusted.</p><p>MATERIALS AND METHODS</p><p>Stillase</p><p>Stillage from typical pilot-plant operations was obtained as describedpreviously (1). Large batches (200 litres) were divided into 4-litre lots whichwere stored frozen until required. Thawed stillage was then maintained at 4Cuntil it was transferred into the digester's feed container, where a magneticstirrer ensured that the suspended material would be evenly fed into the digesteritself. To prevent fungal growth an anaerobic atmosphere was maintained above thefeed. In preparing the stillage for feeding into the digester, the sulphateconcentration was modified by barium precipitation, and additions of sodiumhydroxide and various nutrients were made, as described below.</p><p>Sulphate Concentration: The sulphate remaining in the stillage is a function ofthe temperature at which the hydrolysis liquor is neutralised. The temperatureused in the pilot-plant process was 80C, which gave sulphate concentrations ofapproximately 1800 mg 1~ . Commercially, neutralisation can be 140C, resulting in sulphate concentrations of approximately 500 mg 1To simulate the effects of commercial practice the sulphate concentration wasreduced to approximately 500 mg 1 by precipitation with barium chloride.</p><p>398</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Dal</p><p>hous</p><p>ie U</p><p>nive</p><p>rsity</p><p>] at</p><p> 23:</p><p>59 0</p><p>4 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>A 10% solution of BaCl2.2H20 was used to precipitate a stoichiometric quantityof sulphate. After mixing for 15 minutes to ensure that the reaction was complete,the barium sulphate precipitate was removed from the suspension by vacuumfiltration through Whatman No. 1 filter paper.</p><p>Nutrient Addition: During the course of this study the stillage wassupplemented with various concentrations of nitrogen (N), phosphorus (P),potassium (K), magnesium (Mg), and iron (Fe) as AR-grade urea, NH4H2P0^,KC1, HgCl2.6H20, and FeCl3.6H2O, respectively. General methanogenicfermentation indicators along with analyses of the digester effluent for solublenutrient concentrations and analyses of digester contents for precipitateaccumulation, were used to assess the requirements for these added nutrients.</p><p>Alkalinity Addition: To maintain the digester pH above 6.80 an alkalinityaddition was required. A 20% NaOH solution was added to the stillage followingsulphate removal and nutrient addition. At low organic loading rates (</p></li><li><p>The concentration of H2S in the gas was determined using Drager tubes (CH28201) in conjunction with a Drager hand pump (Dr'agerwerk A.G., Lubeck, FRG).</p><p>Analytical methods used to determine the Chemical Oxygen Demand (COD), metals,total nitrogen and phosphorus, have been described in an earlier publication (1).</p><p>Methods of Calculation</p><p>The concentration of total soluble sulphides in the digester was calculatedusing the technique of Lawrence et al (16).</p><p>The true growth yield and the endogenous decay coefficient were calculatedusing the following equations (17,18):</p><p>" V Yt t</p><p>whereju ~c</p><p>where: </p></li><li><p>Figure 1: Chronological plots of digester operating conditions;</p><p>(a) digester pH and alkalinity(b) volatile acid concentrations and organic loading rate (the levels</p><p>of key inorganic species are shown in tabular form)(c) soluble nitrogen and phosphorus concentrations</p><p>(a)'</p><p>M 7-0-tuaa</p><p>00</p><p>a. _ 40057</p><p>o Alkalintly</p><p>1 0 0</p><p>ACCLIMATION PHASE</p><p>I - ) &gt;</p><p>( ) P</p><p>200</p><p>OAYS</p><p>NUTRIENTADJUSTMENT</p><p>PHASE</p><p> lie acid</p><p>ociomc acid</p><p>INCREASEDLOADING RATE</p><p>PHASE</p><p>'8?5 E</p><p>2S</p><p>S O * ' mql"</p><p>N.....,/-'</p><p>Pd.d,r'</p><p>P.dual mgi"'</p><p> g i - '</p><p>,....,!-'</p><p>: addadmgi"1</p><p>1950 | 70</p><p>240</p><p>120</p><p>300</p><p>4 8 0</p><p>2 4 0</p><p>~ 10</p><p>20</p><p>30</p><p>50</p><p>I 365I s| 194</p><p>4 3 0</p><p>120</p><p>120</p><p>To[en</p><p>400 1 500 1</p><p>0</p><p>' 0</p><p>0</p><p>(c)</p><p>OAYS 0</p><p>30 E</p><p>401</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Dal</p><p>hous</p><p>ie U</p><p>nive</p><p>rsity</p><p>] at</p><p> 23:</p><p>59 0</p><p>4 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>Figure 2: Chronological plots of digester operating conditions;</p><p>(a) biogas production(b) sludge activity(c) percentage total and soluble COD removal</p><p>(a)</p><p>zO 10</p><p>i </p><p>Co)</p><p>8 0-2-</p><p>o</p><p>200</p><p>OArs</p><p>200</p><p>DAYS</p><p>(c)</p><p>O 40</p><p>luble COO</p><p>ial COO rn</p><p>DAYS</p><p>402</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Dal</p><p>hous</p><p>ie U</p><p>nive</p><p>rsity</p><p>] at</p><p> 23:</p><p>59 0</p><p>4 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>Figure 3: Chronological lots of digester operating conditions;</p><p>(a) suspended solids concentrations(b) volatile suspended solids to total suspended solids ratio(c) solids and hydraulic retention times</p><p>In reactor</p><p>a Total itiipandttd ao</p><p>*upiindd</p><p>(c )</p><p>O O D VSS / TSS Sno</p><p>* * Ettlutnt VSS / TSS Rilio</p><p>200</p><p>DAYS</p><p>200</p><p>DAYS</p><p>403</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Dal</p><p>hous</p><p>ie U</p><p>nive</p><p>rsity</p><p>] at</p><p> 23:</p><p>59 0</p><p>4 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>raw stillage: nitrogen, 240 me 1 ; phosphorus, 120 mg 1 ; potassium20 mg 1~ ; magnesium, 30 m g l ; iron, 40 mg 1 . The stillage sulphateconcentration was 1950 mg 1 and no sulphate removal was performed.</p><p>Initially the reactor performed satisfactorily as shown by the reduced acetateand propionate concentrations achieved by day 30 (Fig. lb). However, despiteconsistent feeding techniques, organic loading rates, and nutrient additions,propionate began to rapidly accumulate in the digester after day 30, causing adrop in the digester pH from 7.20 to 6.90. The soluble sulphide concentration atthis time was estimated to be 190 mg 1-1 and hence it was concluded thatsulphide inhibition caused the propionate accumulation. This conclusion issupported by the fact that when the sulphate concentration in the feed stillagewas reduced from 1950 to 70 mg 1 on day 58 using barium precipitation, a rapiddecrease in the propionate concentration was observed over the next 12 days, sothat by day 80, satisfactory operation was again achieved (Fig. lb).</p><p>For the remainder of the study, the sulphate concentration in the feedstillage was lowered to approximately 500 mg 1 before digestion to simulate theeffect of high temperature neutralisation which normally would be performed in acommercial plant. The required sulphate concentration range was achieved althoughthe actual levels varied over the range 190 to 500 mg 1~ (Fig. lb). On day 120,towards the end of the acclimation phase, a second rapid accumulation ofpropionate occurred which had no known cause (the organic loading rate was still1 kg COD m~3 day"1 and other operating conditions had remained unchanged fromday 0). The propionate concentration then peaked at day 130, but by day 155 hadreturned to a satisfactorily low level. Sulphide toxicity was considered anunlikely cause since gas analysis performed on day 135 detected only 18 ppmhydrogen sulphide, equivalent to a total soluble sulphide concentration of 68mg 1-1. This is below the toxic concentration range of 100-150 mg 1-1 fortotal soluble sulphide (19-22).</p><p>Until day 110, because the feed container was unmixed and much of the addedphosphorus was precipitating, the actual concentration of phosphorus fed into thedigester was only c. 10 mg 1-1 (Fig. lb). Doubling the phosphorus addition(from 120 to 240 mg 1-1) on day 78 did not result in an increase in solublephosphate. Hence, from day 110 the level of added phosphorus was returned to 120mg 1-1 and the feed container was magnetically stirred to ensure that suspendedmaterial was also fed into the reactor.</p><p>Nutrient Adjustment Phase (Days 161 to 220)</p><p>Although the nutrient supplements were modified a number of times during thestudy, the phase of the experiment from day 161 to day 220 was called the nutrientadjustment phase since decisions on all subsequent nutrient additions werefinalised during this phase.</p><p>From day 161 to day 220 the organic loading rate was held at 1.5 kg CODm"3 day"1. Satisfactory operation of the digester was indicated by acetateand propionate concentrations less than 30 and 20 mg I"1, respectively, and by adigester pH of 6.95-7.00 at alkalinities of 3.3-3.7 g CaCO3 I"</p><p>1 (Fig. la).Over the same period approximately 5 1 day"1 of biogas were produced with totalCOD removal ranging from 70% to 77%, while soluble COD removal was consistentlybetween 86.3% and 87.2% (Fig. 2a,c). Sludge activity was also stable, fallingwithin the range 0.14 to 0.15 g COD removed g VSS-1 day-1 (Fig. 2b). Thereactor biomass concentration varied from 8.7 to 9.1 mg VSS 1-1 (Fig. 3a).</p><p>404</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Dal</p><p>hous</p><p>ie U</p><p>nive</p><p>rsity</p><p>] at</p><p> 23:</p><p>59 0</p><p>4 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>From day 110, nitrogen and phosphorus additions had been held constant at 430and 120 rag 1~^, respectively. Since subsequent analyses of the concentrationsof nitrogen and phosphorus in the soluble digester established that thesenutrients were being supplied in excess (Fig. la), the levels of supplementationremained unchanged during the experiment. However, the addition of the othernutrients (potassium, magnesium, and iron) ceased on day 209 because analyses forthese elements in the soluble effluent from the digester and' in the digester'ssuspended solids on day 157 revealed soluble potassium and magnesium levels (42and 44 mg l'l, respectively) well in excess of the added levels. Furthermore,in the digester's suspended solids iron was present at a concentration of 3120 mg1~1, indicating its accumulation by precipitation with other inorganic species.These data clearly established that the additions of potassium, magnesium, an...</p></li></ul>