Role of agitation conditions in nitrification

The objective of this study was to determine the role of agitation conditions in the oxidation of nitrite ions by Nitrobacter. Batch reaction kinetic experiments were conducted in baffled stirred tanks. The range of agitation conditions studied was 6200 ? 95700 ergs/cm³ sec. This power input corresponds to 3.2 ? 45.6 hp/ 1000 gal, or a “hem Scale” of 3 ? 9. After a lag phase, the reaction kinetics were found to be zero order with respect to nitrite over a concentration range of 590 to 10 mg/liter nitrite nitrogen (NO₂^?-N). The zero-order rate constants were found to significantly decrease with increasing impeller power input per volume of liquid (P / V).     

An energy cost minimizing strategy for fermentation dissolved oxygen control

A cost-minimizing mathematical model for on-line control of dissolved oxygen using agitation speed and aeration rate was developed. In pilot scale monensin fermentation using Streptomyces cinnamonensis, this algortihm provided stable control of dissolved oxygen at 40%, reducing energy usage 27.8%. The agitation and aeration profiles provided by the algorithm respresent the pathway of least energy cost for control at the desired dissolved oxygen level. Other observed advantages of bivariable control were reduction of foaming, evaporation, and gas holdup. Reduced maintenance of compressors and agitator motors could also be expected due to decreased load. Monensin productivity equivalent to fermentation with constant agitation and aeration was not obtained, however, with potency reduced 14.8% with the dissolved oxygen control strategy.List of Symbols A m² cross sectional area of fermentor - A ₁, A ₂, A ₃, A ₄ constants of polynomial fit to Calderbank's equations - BP N/m² gauge back pressure - C _ag $/W/s cost of electrical power - C _Q $/m³ cost of compressed air - CE mol/m³/s carbon dioxide evolution rate - D m impeller diameter - DO, DO _meas, DO _sp % dissolved oxyen saturation at any time, measured, and setpoint respectively - h m height of liquid in fermentor - H N/m²/mmol Henry's constant for oxygen in water - H _av average gas holdup in fermentor - k _L a, k _L a _meas, k _L k _sp s^–1 oxygen mass transfer coefficient at any time, measured, and setpoint respectively - N, N _sp s^–1 agitation speed at any time and setpoint respectively - N _a, N _{a, sp} aeration number at any time and setpoint respectively - N _i total number of impellers - N _p impeller power number - N _s number of impellers into which air is directly sparged - OU, OU _meas mol/m³/s Oxygen uptake rate at any time and measured respectively - P W ungassed agitation power - P _g, P _g,meas, P _g,sp W gassed agitation power at any time, measured, and set point respectively - Q, Q _meas, Q _sp m³/s aeration rate at any time, measured, and setpoint respectively - T K fermentation temperature - u _g m/s linear gas velocity - V m³ fermentation liquid volume - mole fraction of oxygen in fermentation off-gas - calculation constant - motor efficiency - $/s sum of agitation and aeration costs - kg/m³ liquid density     

Oxygen transfer in a stirred loop fermentor with dilute polymer solutions

Oxygen transfer in a 0.35 m diameter stirred loop fermentor (a stirred tank with a concentric draft tube) has been studied with water containing a small amount of polymer(polyethylene oxide) as a drag-reducing additive.Power consumption was measured. It was found that the addition of polyethylene oxide causes an increase of power consumption. This is contrary to the results reported in the literature.Volumetric mass transfer coefficients (K _La) were measured. In water the introduction of the draft tube increased the K _La coefficient. The increase in K _La became larger with impeller speed. On the other hand, mass transfer in dilute polymer solutions decreased due to the presence of the draft tube. An empirical correlation has been proposed for the volumetric mass transfer coefficient in stirred loop fermentors. It has a general applicability.List of Symbols a 1/m specific surface area - C constant in Eq. (6) - g m/s² gravitational acceleration - K _L m/s overall liquid-phase mass transfer coefficient - n 1/s impeller speed - P W aerated power input by mechanical agitation - P _g W power input by sparged air - Q m³/min volumetric gas flow rate - U _sg m/s superficial gas velocity - V m³ liquid volume Greek Symbols exponents in Eq. (3) - exponent in Eq. (6) - kg/m³ density     

Critical impeller speed for solid suspension in turbine agitated contactors

The present study in solid-liquid contactors, an attempt has been made to calculate the minimum/critical impeller speed required for complete suspension of solids. A new correlation, involving Reynolds number, modified Froude number, along with the agitation characteristics is proposed. The effect of impeller geometry as well as impeller clearance are clearly established for 6-blade (flat) turbine agitated contactors.List of Symbols B Solid weight fraction (%) - c Clearance of the impeller from the tank bottom (m) - d _P Average particle size(m) - d _R Impeller diameter (m) - d _T Vessel diameter (m) - g Acceleration due to gravity m/sec₂ - N _cs Critical impeller speed (S^–1) Greek Letters Kinematic viscosity m²/sec - _L Density of liquid kg/m³ - _S Density of solid kg/m³ - Density difference between solid and liquid kg/m³     

Fermentation ofCandida utilis for uricase production

Summary Conditions for the production of microbial uricase byCandida utilis were studied. For the selected strain, hypoxanthine proved to be the most effective inducer of uricase formation. The highest values of biomass as well as uricase activity in the mechanically agitated fermentor were obtained under the following conditions: 50 h, rotation impeller speed 7 s^–1, air flow rate 1.25×10^–5 m³s^–1, concentration of inducer 0.1%.List of symbols b width of baffle, m - c length of baffle, m - D diameter of cylindrical fermentor, m - d diameter of impeller, m - d ₁ diameter of impeller disc, m - Fr _m impeller Froud number - g gravitional acceleration, ms^–2 - H height of batch surface above bottom, m - H ₂ height of impeller disc above bottom, m - h height of impeller blade, m - Kp _g flow rate number - L length of impeller blade, m - N rotational speed of impeller, s^–1 - Re _m impeller Reynolds number - T time, h - V volume of batch, m³ - V _g air (gas) flow rate, m³s^–1 - x mass fraction of the dry matter of cells - x ₀ initial value of the mass fraction of the dry matter of cells - _r volume fraction of the dry matter of cells - <eta<₁ viscosity of pure liquid, Pa s - viscosity of batch (suspension of microbial suspension), Pa s - density of batch, kg m^–3     

Application of fuzzy multiobjective optimization for self-sucking impellers in a bioreactor

For three types of self-sucking impellers (fourand six-pipe and disk impellers) mixing power, initial point, amount of gas leaving the impeller and mass transfer coefficient were determined experimentally. Investigations were performed for two systems: water and biomass solution.From the point of view of a minimum mixing power and maximum mass transfer coefficient the best impeller has been chosen. Fuzzy multiobjective optimization for determination of optimum operating conditions is proposed.List of Symbols c concentration of oxygen - D tank diameter - d impeller diameter - g acceleration of gravity - H height of liquid in the tank - H height of liquid above impeller, H=H-y - k consistency coefficient - k _L a volumetric mass transfer coefficient - N rotational speed of impeller - n flow behaviour index - P mixing power for pure liquid - P _G mixing power for aerated liquid - V _G volumetric air flow rate - y distance of impeller from the tank bottom - v _a apparent kinematic viscosity of liquid - density of liquid - time - gas hold-up - Eu=P/N ³ d ⁵ or Eu_G=P _G /N ³ d ⁵ Euler Number for non-gassed or aerated liquid - Fr=N ² d/g Froude Number - Fr^*=N ² d ² /g(H -y) modified Froude Number - K_G=V _G /N d ³ gas flow number - Re=N d ² /v _a Reynolds Number - Sh=k _K a/(g ² /v _a )^1/3 Sherwood Number     

Hydrodynamic characteristics and mixing behaviour of Sclerotium glucanicum culture fluids in an airlift reactor with an internal loop used for scleroglucan production

The filamentous fungus, Sclerotium glucanicum NRRL 3006, was cultivated in a 0.008 m³ airlift bioreactor with internal recirculation loop (ARL-IL) for production of the biopolymer, scleroglucan. The rheological behaviour of the culture fluid was characterised by measurement of the fluid consistency coefficient (K) and the flow behaviour index (n). Based on these measurements, the culture fluid changed from a low viscosity Newtonian system early in the process, to a viscous non-Newtonian (pseudoplastic) system. In addition, reactor hydrodynamics and mixing behaviour were characterised by measurement of whole mean gas hold-up (ɛ _g), liquid re-circulation velocity (U _ld) and mixing time (t _m). Under identical process conditions, the effects of the viscosity of the culture fluid and air flow rate on ɛ _g, U _ld and t _m were examined and empirical correlations for ɛ _g, U _ld and t _m with both superficial velocity U _g and consistency coefficient K were obtained and expressed separately. The correlations obtained are likely to describe the behaviour of real fungal culture fluids more accurately than previous correlations based on Newtonian or simulated non-Newtonian systems. Journal of Industrial Microbiology & Biotechnology (2001) 27, 208–214. Received 05 June 2000/ Accepted in revised form 18 March 2001     

Process engineering aspects of the bioleaching of copper ores

The bioleaching of minerals is a complex process that is affected by a number of biological, mineralogical, electrochemical and engineering factors. This work presents and discusses the most significant process engineering aspects involved in the bacterial leaching of copper ores, i.e. bacterial population, type of mineral and particle size, nutrients and inhibitors, oxygen and carbon dioxide, temperature and pH, leaching kinetics and operation mode.It is concluded that more work is needed in this area in order to gain a deeper insight in the many factors that govern this process. This would allow to significantly improve its overall productivity.List of Symbols C _L kg/m³ dissolved oxygen concentration - C ^* kg/m³ equilibrium oxygen concentration - d, e, f, g % percentage of C, H, O and N in the cell - D m impeller diameter - K consistency index - K _S, K₁, K_c constants - k _La h^–1 volumetric oxygen transfer coefficient - M _b mol/kg biomass apparent molecular weight - N s^–1 rotation frequency - n behavior index - P kg/m³ ungassed agitation power, product concentration - P _g kW/m³ gassed agitation power - p % pulp density - Q m³/h air flow rate - S kg/m³ limiting substrate concentration - W kg/(m³ · h) mass transfer rate per unit volume - X cells/cm³ biomass concentration - Y _o g cells/g Fe oxygen cell yield - Y _x g cells/g Fe substrate cell yield - h^–1 specific growth rate - _m h^–1 maximum specific growth rate     

Diurnal changes in needle gas exchange in alpine Pinus pumila during snow-melting and summer seasons

Pinus pumila (Pallas) Regel. is a dominant dwarf tree in alpine regions of Japan. The possible factors limiting the net photosynthetic rate (P_n) of the needles of P. pumila were examined in the snow-melting (May) and the summer (August) seasons. In August, in situ maximum P_n was 20 mol kg^–1 needle s^–1 in the current-year needles and 25 mol kg^–1 needle s^–1 in the 1-year-old needles. Diurnal trends of P_n in August were positively related to fluctuations in photosynthetic photon flux density (PPFD) and no midday depression of P_n was found, indicating that a decrease in PPFD rather than an increase in needle-to-air vapor pressure deficit (W) might cause the reduction of P_n. Both stomatal conductance (g_s) and P_n were lower in May than in August. In May, P_n and g_s were almost zero in the morning, but gradually increased with decreasing W, reaching maximum P_n values (4 mol kg^–1 needle s^–1) and g_s (60 mmol kg^–1 needle s^–1) at 16.00 hours. The daytime P_n in May was positively related to g_s. Relative water content in the exposed needles above the snow in May was 83%, which was far above the lethal level. This indicates that the water flow from stems or soils to needles was enough to compensate for a small amount of water loss due to the low g_s in May, although the water supplied to needles would be impeded by the low temperatures. Thus, the reduced g_s in May would be important for avoiding needle desiccation, and would result in a reduced P_n.     

Anchorage-dependent animal cell culture by using a porous microcarrier

CHO-K1 cells were cultured by using a porous microcarrier. The effects of microcarrier concentration and agitation rate on cell growth in porous microcarrier cultures were investigated. The specific growth rate of 0.041 h^–1 in porous microcarrier cultures was independent of both microcarrier concentration and agitation rate. By estimating the total surface area occupied by cells from the maximum cell number, it was found that not all the surface area of the porous microcarrier was utilizable for cell growth.The maximum cell number decreased with increasing the microcarrier concentration and the agitation rate. From this result, it was also found that not all the cells grown on the interior surface of the porous microcarrier were protected against mechanical damage due to agitation. The protection capacity of the porous microcarrier was estimated to be 300 cells/carrier. The direct gas sparging into the culture broth in porous microcarrier cultures improved the cell density without mechanical damage to animal cells.List of Symbols d m microcarrier diameter - d _i m impeller diameter - d _p m mean pore diameter - n _i s^–1 agitation rate - p Pa pressure difference - v m/s velocity of microcarrier - v _p m/s average velocity flowing through cyclinder - Pa · s viscosity of medium - angle measured from stagnant point - Pa average shear stress - Pa shear stress distribution     

Improvement of foam breaking and oxygen-transfer performance in a stirred-tank fermenter

This study examined a stirred-tank fermenter (STF) containing low-viscosity foaming liquids with an agitation impeller and foam-breaking impeller mounted on the same shaft. Results showed that the performance of the foam-breaking impeller can be improved by changing a conventional six-blade turbine impeller into a rod impeller as the agitation impeller. The volumetric oxygen-transfer coefficient, k _L a, in the mechanical foam-control method (MFM) using a six-blade vaned disk as the foam-breaking impeller in the STF with the rod impeller was approximately five times greater than that of the chemical foam-control method (CFM) adding an anti-foaming agent in the STF with the six-blade turbine impeller. Application of the present method to the cultivation of Saccharomyces cerevisiae K-7 demonstrated that the cultivation time up to the maximum cell concentration was remarkably shorter than that achieved using a conventional CFM.     

The influence of mechanical forces on the morphology and penicillin production of Penicillium chrysogenum

The influence of mechanical forces resulting from the rotation of (multiple) turbine impellers on the morphology and penicillin production of Penicillium chrysogenum Panlabs P-1 was investigated in batch fermentations using semi-defined media. Experiments were carried out at three different scales of fermentation, 5 dm³,100 dm³ and 1000 dm³ working volume, with the impeller tip speed ranging from 2.5 to 6.3 m/s. Throughout all fermentations, the dissolved oxygen concentration never fell below the critical value for maximum penicillin production. Morphological measurements using image analysis showed that the mean main hyphal length and mean hyphal growth unit increased during the rapid growth period and then decreased to a relatively constant value dependent on the agitation intensity. The specific rate of penicillin production (q _pen)and the average main hyphal length during the linear penicillin production phase were lower at high agitation speed, which promoted more rapid mycelial fragmentation and a higher branching frequency. Comparison of the results from the three scales showed that impeller tip speed is a poor scale up parameter whereas a term based on mycelial circulation through the zone of high energy dissipation fitted the data well.List of Symbols C.E.R. mmol/(dm³h) Carbon dioxide evolution rate - D m Impeller diameter - D.O.T. % air saturation Dissolved oxygen tension - L _e m Mean effective length or main hyphal length - O.U.R. mmol/(dm³h) Oxygen uptake rate - P W Total power dissipation - q _pen units/(mg dry cell weight h) rate Specific penicillin production - R.Q. Respiratory quotient - 1/t _cs^–1 Circulation frequency     

Determination of power consumption and volumetric oxygen transfer coefficient in bioreactors

A torque meter has been developed for determining the power consumption in a bench stirred tank. The device has been bonded in the stirrer shaft inside a commercial bench fermentor, in order to avoid frictional losses in the mechanical seal. Power consumption measurements in ungassed and gassed systems were obtained at different agitation and aeration conditions, for Newtonian and non-Newtonian fluids. Also, a "simple modified sulfite method" for volumetric oxygen transfer coefficient (k_La) determination was developed and the experimental data were correlated with the gassed power (P_g) by using well-known correlations presented in the literature.     

Power input measurements in a production scale bioreactor

Summary Power input measurements are carried out in a production bioreactor with a liquid volume up to 25 m³. The results show that the cavity formation principle is applicable to reactors at this scale. It can also be observed that empirical correlations are not useful to predict gassed power input accurately. It is found that at gas flow rates for normal production conditions (N_Q =0.1), the gassed power input is about 30–40 % of the non gassed power input.Nomenclature C_p specific heat J/kgK - D impeller diameter m - D_b1 impeller blade diameter m - d baffle diameter m - Fr Froude number - - g gravitation m/s² - h impeller clearance m - H liquid height m - N stirrer speed s^-1 - N_p power number - - N_Q gas flow (aeration) number - - N_Q ^* critical gasflow number for 3 cavity formation - - P_o ungassed power consumption W - P_g gassed power consumption W - Q gas flow rate (273 K, 10⁵ N/m²) m³/s - Re Reynolds number - - T tankdiameter m temperature K - t time s - V liquid volume m³ - ^Vtip impeller tip speed m/s - V_s impeller correlated superficial gas flow rate m/s - W impeller blade width m - density kg/m³     

Growth and death rates of bovine embryonic kidney cells in turbulent microcarrier bioreactors

Bead-bead collisions have been characterized using the velocity of the smallest turbulent eddies to calculate a turbulent collision severity (defined as the energy of collisions times their frequency), but a shear-based collision mechanism with a different dependence on the system variables is also applicable. This shearbased mechanism and the ratio of smallest eddy size to microcarrier diameter can explain the beneficial effects of both smaller diameter microcarriers and higher viscosity of the medium on the growth rate of bovine embryonic kidney cells. Death rates of these cells have also been measured at several levels of agitation. The decrease in apparent growth rate from increasing agitation is caused both by a higher rate of cell death as well as a lower intrinsic growth rate.List of Symbols B unspecified biological variable - d cm bead diameter - d _i cm impeller diameter - e error in estimate of power number - F _n , F _s (g·cm)/s² normal and shear forces on a cell - Fr Froude number - g 980cm/s² acceleration of gravity - k k^–1 first order death rate constant - m g mass of a bead - n s^–1 impeller rotational rate - n _b number of impeller blades - N _p impeller power number - R _i cm impeller leading edge radius - TCS (g·cm²)/s³ turbulent collision severity - V cm³ reactor volume - v _br cm/s rms relative velocity between beads - v _e cm/s velocity in smallest eddies - X number of cells/cm₃ cell population Greek Symbols volume fraction microcarriers - s^–1 shear rate - cm²/s³ turbulent power dissipation rate - cm size of smallest eddies - g/(cm·s) dynamic viscosity - h^–1 apparent growth rate of cells - ₀ h^–1 intrinsic growth rate of cells in absence of death - v cm²/s kinematic viscosity - _b g/cm³ bead density - _f g/cm³ fluid density - g/(cm·s²) shear stress     

Development and evaluation of Trichoderma asperellum preparation for control of sheath blight of rice (Oryza sativa L.)

Sheath blight, which is caused by Rhizoctonia solani, is a disease that majorly impacts rice production. A biocontrol agent used for control rice sheath blight must be sprayed on the stem at specific times during rice growth, a process that is labour-intensive and renders the antagonist vulnerable to environmental factors. In this study, Trichoderma asperellum T12 was used to produce preparation by solid-state fermentation using a surface-response method. Rice hull was selected as a carrier based on its ability to sustain the T12 floating in the water and protect T12 from ultraviolet irradiation. The production of a T12-based preparation required 32% wheat bran, 7% inoculum, 2.3 g kg^?1 (NH₄)₂SO₄ and 65% water content, with fermentation at 27.5°C for 30 days and agitation every six days. The preparation demonstrated 90% biocontrol efficacy and significantly (P > 0.05) increased the seed-set rate and 1000-grain weight as compared with the pathogen treatment. The population of Trichoderma on the surface of rice leaf sheath in the treatment applied with T12 preparation increased from 232 cfu (colony forming units) g^?1 fw (fresh weight) to 436 cfu g^?1 fw during rice growth stage, which was significantly (P > 0.05) higher than pathogen treatment. The population of R. solani on the leaf sheath increased from 41 cfu g^?1 fw to 271 cfu g^?1 fw in the pathogen treatment, while remained stable (P > 0.05) at level of 10–23 cfu g^?1 fw in T12 preparation applied treatment. Biocontrol of sheath blight by the addition of the preparation to the soil is effective and decreases the costs of agro-industrial waste disposal.     

Oxygen transfer correlation in high cell density culture of recombinant E. coli

Summary A recombinant E. coli BL21[pET3a-T2M2] was cultivated in fed-batch cultures and cell mass increased to more than 70g/L. The volumetric oxygen transfer coefficient was estimated in a range of various fermentation parameters (agitation speed, oxygen flow rate and cell mass concentration) and finally the oxygen transfer correlation in bioreactor containing the recombinant E. coli cultures was determined as: k_spla = 0.0195 (P_g/V)^0.55 (V_s)^0.64 (1+2.12X+0.20X²)^–0.25.     

Optimisation of agitation and aeration in fermenters

The problem of optimising agitation and aeration in a given fermenter is addressed. The objective function is total electric power consumed for agitation, compression and refrigeration. The major constraint considered is to ensure that the dissolved oxygen concentration is above the critical value. It is shown that it is possible to analytically calculate the optimal pair (air flowrate, stirrer speed) and that, at least for the industrial antibiotics fermentation used as case-study, the optimum lies within a window for satisfactory operation, limited by other possible constraints to the problem. Savings achievable by optimal operation as compared with current industrial procedure were found to be around 10% at pilot plant scale (0.26 m³) and 20% at full scale (85 m³).List of Symbols A fermenter cross sectional area (m²) - C dissolved oxygen concentration (mole m^–3) - C ^* DO concentration in equilibrium with the gas (mole m^–3) - C _crit critical DO concentration (mole m^–3) - C _p specific heat of air at constant pressure (J kg^–1 K^–1) - C _sp dissolved oxygen set point (mole m^–3) - C _v specific heat of air at constant volume (J kg^–1 K^–1) - D agitator diameter (m) - f pressure correction of air flow-rate - (Fl _g)_F aeration number at flooding - (Fr _g)_F froude number at flooding - k coefficient in expression for mass transfer coefficient - K _La volumetric oxygen transfer coefficient (s^–1) - m power exponent in expression for mass transfer coefficient - n gas flow rate exponent in expression for mass transfer coefficient - n ^* number of impellers - N rotation speed (s^–1) - N _F rotation speed at flooding (s^–1) - N _p unaerated power number - N _pg aerated power number - OUR Oxygen Uptake Rate (mole m^–3 s^–1) - p ₀ atmospheric pressure (N m^–2) - p ₁ compressor exit pressure (N m^–2) - p ₂ pressure at the bottom of the fermenter (N m^–2) - p ₃ pressure at the top of the fermenter (N m^–2) - P _c compression power (W) - P _d power added by expansion (W) - P _ev power removed by evaporation (W) - P _g agitation power (W) - P _m power added by metabolism (W) - P _r power removed by refrigeration (W) - P _t total power (W) - Q air flow-rate at atmospheric conditions (m³ s^–1) - Q _f air flow-rate at average fermenter conditions (m³ s^–1) - s ₀ absolute humidity at atmospheric conditions - s ₃ absolute humidity at fermenter exit - T tank diameter (m) - V liquid volume (m³) - v _s gas superficial velocity (m s^–1) - _i parameter defined in the text - safety margin for dissolved oxygen (mole m^–3) - ratio of specific heats of air - _g agitation efficiency - _c compression efficiency - _r refrigeration efficiency - liquid density (kg m^–3) - _g air density (kg m^–3) - latent heat of vaporisation of water (J kg^–1) The authors are grateful to Elsa Silva, Carlos Lopes, Carlos Aguiar, Fernando Mendes, and Alexandre Cardoso, who helped with parts of this work, and to CIPAN for permission to publish these data.     

Utilisation of soil organic P by agroforestry and crop species in the field,western Kenya

A field experiment in western Kenya assessed whether the agroforestry species Tithonia diversifolia (Hemsley) A. Gray, Tephrosia vogelii Hook f., Crotalaria grahamiana Wight & Arn. and Sesbania sesban (L) Merill. had access to forms of soil P unavailable to maize, and the consequences of this for sustainable management of biomass transfer. The species were grown in rows at high planting density to ensure the soil under rows was thoroughly permeated by roots. Soil samples taken from beneath rows were compared to controls, which included a bulk soil monolith enclosed by iron sheets within the tithonia plot, continuous maize, and bare fallow plots. Three separate plant biomass samples and soil samples were taken at 6-month intervals, over a period of 18 months. The agroforestry species produced mainly leaf biomass in the first 6 months but stem growth dominated thereafter. Consequently, litterfall was greatest early in the experiment (0–6 months) and declined with continued growth. Soil pH increased by up to 1 unit (from pH 4.85) and available P increased by up to 38% (1 g P g^–1) in agroforestry plots where biomass was conserved on the field. In contrast, in plots where biomass was removed, P availability decreased by up to 15%. Coincident with the declines in litterfall, pH decreased by up to 0.26 pH units, plant available P decreased by between 0.27 and 0.72 g g^–1 and P_o concentration decreased by between 8 and 35 g g^–1 in the agroforestry plots. Declines in P_o were related to phosphatase activity (R²=0.65, P<0.05), which was greater under agroforestry species (0.40–0.50 nmol MUB s^–1 g^–1) than maize (0.28 nmol MUB s^–1 g^–1) or the bare fallow (0.25 nmol MUB s^–1 g^–1). Management of tithonia for biomass transfer, decreased available soil P by 0.70 g g^–1 and P_o by 22.82 g g^–1. In this study, tithonia acquired P_o that was unavailable to maize. However, it is apparent that continuous cutting and removal of biomass would lead to rapid depletion of P stored in organic forms.