BACKGROUND OF THE INVENTION The present invention relates mainly to a water treatment control apparatus that controls water quality of treated water in a sewage treatment plant. Nowadays, a response to environmental problems is required, and also in the 5 sewage treatment plant, energy saving is further requested in addition to improvement in water quality of treated water discharged to a public water area. In the sewage treatment plant, organic matters or nitrogen in sewage are removed by using a microorganism suspension called activated sludge. A reactor tank for supplying air to activated sludge by a blower is called an aerobic tank. In the aerobic tank, organic matters 10 are incepted and/or consumed, and are removed through an anabolism reaction and/or a catabolism reaction due to microorganisms. Most of nitrogen in inflow sewage are contained in an ammonia nitrogen form, and are oxidized to nitrate-nitrogen through nitrification bacteria in the presence of oxygen. A part of the nitrate-nitrogen remains in return sludge and is returned to the upstream side. At that time, a denitrification reaction for reduction to a nitrogen gas is 15 caused and a nitrogen component is removed. On the other hand, when ammonia nitrogen remains in discharge water due to shortage of nitrification, an influence on water creatures in a discharged water area or consumption of dissolved oxygen (DO) is feared. Therefore, an appropriate management for a nitrification reaction is required to keep an environment of a discharge destination. For this purpose, it is necessary to appropriately control supply of air 20 volume by a blower that consumes much power. When the air volume supply amount is not sufficient, adverse influences on an environment due to shortage of nitrification are caused. Alternatively, when the air volume supply amount is excessive, the air volume is supplied in vain also after completion of nitrification, and therefore power consumption increases. For control of sewage treatment, DO control is used in which DO of a DO meter 25 that is installed at the end on the downstream side of the aerobic tank is used as a control index. A blower air volume is controlled so as to keep constant the DO of the DO meter that is installed at the end on the downstream side of the aerobic tank. As a result, activity of microorganisms is kept, and removal of organic matters and the nitrification reaction are controlled (for example, "Sewerage facility plan.design manual and comment" year 2009 version, Publication Office, 30 Japan Sewage Works Association; hereinafter, referred to as Literature 1). Recently, a precision of an ammonia meter for ~neasuringa mmonia nitrogen - 3 - concentration in activated sludge is improved, or controllability of a blower having a small capacity suitable for a separate biological reactor is improved. Thereby, a control method for using an ammonia meter is studied for control of the blower air volume to the biological reactor having a single series (for example, Kazuhiro Endo: Development of air distribution amount 5 control system using ammonia meter and do meter, Lecture collection of 47-th sewage system research presentation meeting, pp.9 18-920 (20 10); hereinafter, referred to as Literature 2). When the aerobic tank is considered to be conceptually divided into two of the upstream side and the downstream side, an ammonia meter is installed at the end of the upstream aerobic tank and a DO meter is installed at the end of the downstream aerobic tank. In the case where a measured 10 value of ammonia concentration on the upstream side is larger than a target value, a target value of the DO on the downstream side is increased and the blower air volume is controlled. In the case where the measured value of ammonia concentration on the upstream side is smaller than the target value, the target value of the DO on the downstream side is decreased. Further, since the contact time with air changes due to an inflow flow rate, the target value of the DO is also 15 varied in accordance with increasing and decreasing of the inflow flow rate. In the control method, the DO control is basically used. The target value of the DO is varied in accordance with the ammonia concentration on the upstream side, and thereby attainment of the ammonia concentration is aimed as a target. In a method described in JP-A-20 12- 1 70883 (hereinafter, referred to as Literature 20 3), from a flow rate of sewage flowing in the biological reactor, an air volume to each aerobic tank, and measured values of an ammonia meter installed in each of the aerobic tanks, the air volume to each aerobic tank necessary for a preset nitrification amount between the aerobic tanks is calculated and the nitrification reaction is promoted with the adequate air volume. 25 SUMMARY OF THE INVENTION In a method described in Literature 1, DO is a parameter relating to a reaction activity of microorganisms, but is not ammonia nitrogen itself to be considered in a nitrification reaction. For this purpose, an air volume may be short or excessive due to variations in an inflow flow rate or inflow water quality. 30 In a method described in Literature 2, the air volume to all aerobic tanks is determined from ammonia concentration measured by an ammonia meter installed at the end of the aerobic tank on the upstream side. Therefore, suppose that an ammonia load at the time when inflow sewage flows in that gets to the downstream side than an ammonia meter is larger than an influent ammonia load on the upstream side. In this case, the air volume may be excessive and energy consumption may be large as a whole. On the contrary, suppose that the ammonia load at the time when the inflow sewage flows in that gets to the downstream side than the ammonia meter is smaller than the influent ammonia load on the upstream side. In this case, there is a problem that since the air volume is reduced on the upstream side in which the 5 ammonia load is large, the ammonia load is larger than a processible load at the time of getting to the downstream side, and therefore the discharged water quality deteriorates. In a method described in Literature 3, the ammonia meter is installed in each of the aerobic tanks to thereby perform sophisticated control. However, there is a cost problem that an expensive ammonia meter is similarly installed at the end of the aerobic tank in addition 10 to a DO meter that is recommended to be installed at the end of the aerobic tank in an ordinary sewage treatment plant in Literature 1. Further, the control methods described in Literature 1, Literature 2, and Literature 3 relate to a biological reactor having a single series. Ordinarily, in the sewage treatment to be treated in the biological reactor having a plurality of series, it is not practical in terms of cost that 15 measurement devices or control devices such as a blower required for control are installed in each biological reactor. There is a problem that in these control methods, a control method in the plurality of series is clearly specified. To accomplish the above-described objects, according to one embodiment of the present invention, a water treatment control apparatus includes influent water being water to be 20 treated; a biological reactor in which the influent water flows; an upstream aerobic tank that is located upstream as a part of the biological reactor; a downstream aerobic tank that is located downstream as a part of the biological reactor; an inflow water quality estimation unit that estimates water quality of the influent water; an upstream aerobic tank water quality estimation unit that estimates water quality of the upstream aerobic tank; a downstream aerobic tank water 25 quality estimation unit that estimates water quality of the downstream aerobic tank; an upstream aerobic tank air volume calculation unit that calculates an air volume to the upstream aerobic tank on the basis of estimation results of the inflow water quality estimation unit and the upstream aerobic tank water quality estimation unit; and a downstream aerobic tank air volume calculation unit that calculates an air volume to the downstream aerobic tank on the basis of 30 estimation results of the upstream aerobic tank water quality estimation unit and the downstream aerobic tank water quality estimation unit, wherein water quality estimated by the downstream aerobic tank estimation unit is indicated by dissolved oxygen concentration, and water quality estimated by the inflow water quality estimation unit and the upstream aerobic tank water quality estimation unit contains a substance in which a value varies through oxidation due to oxygen. - 5 - Further, according to another embodiment of the present invention, in the water treatment control apparatus, in a water treatment plant including one or a plurality of influent water group that do not contain the influent water; a biological reactor group in which each of the influent water group flows; an upstream aerobic tank group that is located upstream of each 5 of the biological reactor group; a downstream aerobic tank group that is located downstream of each of the biological reactor group; an influent water group flow rate estimation unit that estimates a total flow rate being a total of a flow rate of the influent water group and the influent water; an upstream aerobic tank group air volume calculation unit that calculates a total upstream aerobic tank air volume to the upstream aerobic tank group and the upstream aerobic tank; a 10 downstream aerobic tank group air volume calculation unit that calculates a total downstream aerobic tank air volume to the downstream aerobic tank group and the downstream aerobic tank; and an influent water flow rate estimation unit that estimates a flow rate of the influent water, a target value of the total upstream aerobic tank air volume calculated by the upstream aerobic tank group air volume calculation unit is a product of the upstream aerobic tank air volume and a 15 ratio between a total flow rate estimated by the influent water group flow rate estimation unit and a flow rate of the influent water estimated by the influent water flow rate estimation unit, and a target value of the total downstream aerobic tank air volume calculated by the downstream aerobic tank group air volume calculation unit is a product of the downstream aerobic tank air volume and a ratio between a total flow rate estimated by the influent water group flow rate 20 estimation unit and a flow rate of the influent water estimated by the influent water flow rate estimation unit. Further, according to yet another embodiment of the present invention, in the water treatment control apparatus, water quality estimated by the inflow water quality estimation unit and the upstream aerobic tank water quality estimation unit contains ammonia nitrogen. 25 Further, according to yet another embodiment of the present invention, the water treatment control apparatus further includes an upstream aerobic tank water quality target value calculation unit that calculates a target value of water quality of the upstream aerobic tank water quality estimation unit on the basis of water quality of the influent water estimated by the inflow water quality estimation unit. 3 0 Further, according to yet another embodiment of the present invention, the water treatment control apparatus further includes a biological reactor air volume calculation unit that calculates a biological reactor air volume to the biological reactor on the basis of an upstream aerobic tank air volume calculated by the upstream aerobic tank air volume calculation unit and a downstream aerobic tank air volume calculated by the downstream aerobic tank air volume calculation unit. Further, according to yet another embodiment of the present invention, in the water treatment control apparatus, in a water treatment plant including one or a plurality of influent water group that do not contain the influent water; a biological reactor group in which 5 each of the influent water group flows; an influent water group flow rate estimation unit that estimates a total flow rate being a total of a flow rate of the influent water group and the influent water; a total biological reactor group air volume calculation unit that calculates a total biological reactor group air volume to the biological reactor group; and an influent water flow rate estimation unit that estimates a flow rate of the influent water, a target value of a total 10 biological reactor group air volume calculated by the biological reactor group air volume calculation unit is a product of the biological reactor air volume calculated by the biological reactor air volume calculation unit and a ratio between a total flow rate estimated by the influent water group flow rate estimation unit and a flow rate of the influent water estimated by the influent water flow rate estimation unit. 15 Further, according to yet another embodiment of the present invention, the water treatment control apparatus further includes a downstream aerobic tank water quality target value calculation unit that calculates a target value of water quality of the downstream aerobic tank water quality estimation unit on the basis of water quality estimated by the upstream aerobic tank water quality estimation unit. 2 0 Further, according to yet another embodiment of the present invention, in the water treatment control apparatus, a target value of water quality of the downstream aerobic tank water quality estimation unit calculated by the downstream aerobic tank water quality target value calculation unit is calculated on the basis of a relationship between downstream difference water quality and downstream target water quality, the relationship between the downstream 25 difference water quality and the downstream target water quality is a relationship between a target value of water quality of the downstream aerobic tank and a difference between water quality of the upstream aerobic tank and treated water target water quality, and from a difference between water quality estimated by the downstream aerobic tank water quality estimation unit and the treated water target water quality, a target value of water quality of the downstream 30 aerobic tank estimation unit is calculated. Further, according to yet another embodiment of the present invention, in the water treatment control apparatus, the downstream air volume calculation unit calculates the downstream aerobic tank air volume on the basis of a target value of water quality of the downstream aerobic tank water quality estimation unit. - 7 - Further, according to yet another embodiment of the present invention, in the water treatment control apparatus, an upstream aerobic tank air volume is calculated by the upstream aerobic tank air volume calculation unit on a basis of a relationship between an air volume and an upstream difference water quality, the relationship between the air volume and 5 the upstream difference water quality is a relationship between the upstream aerobic tank air volume and a difference between water quality of the influent water and water quality of the upstream aerobic tank, and the upstream aerobic tank air volume is calculated from a difference between water quality estimated by the inflow water quality estimation unit and water quality estimated by the upstream aerobic tank water quality estimation unit. 10 Further, according to yet another embodiment of the present invention, the water treatment control apparatus further includes a calculation result display unit that displays a target value of water quality of the upstream aerobic tank water quality estimation unit and a target value of water quality of the downstream aerobic tank water quality estimation unit. Further, according to yet another embodiment of the present invention, in the 15 water treatment control apparatus, the calculation result display unit displays the upstream aerobic tank air volume calculated by the upstream air volume calculation unit and the downstream air volume calculated by the downstream aerobic tank air volume calculation unit. According to the present invention, energy consumption can be suppressed while water quality of a sewage treatment is appropriately controlled. Further, with regard to 20 treatments of a plurality of series, approximately the same control effects as those of a series in which control devices are provided can be exerted. Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 2 5 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating a water treatment control apparatus according to a first embodiment of the present invention; FIG. 2 is a graph illustrating an appropriate nitrification treatment process to a 30 plurality of influent ammonia nitrogen concentration; FIG. 3 is a graph illustrating target ammonia nitrogen concentration to influent ammonia nitrogen concentration; FIG. 4 is a graph illustrating treated ammonia nitrogen concentration to an integrated air volume; FIG. 5 is a graph illustrating target DO of a downstream aerobic tank to ammonia nitrogen load; FIG. 6 is a control flowchart of the first embodiment; FIG. 7 illustrates drawings and calculating formulae illustrating advection of a 5 fluid lump; FIG. 8 is a graph illustrating an air volume distribution function; FIG. 9 illustrates parameters of each fluid lump at time t,; FIG. 10 illustrates an example of a screen display unit; FIG. 11 is a block diagram illustrating a water treatment control apparatus 10 according to a second embodiment of the present invention; FIG. 12 is a block diagram illustrating a water treatment control apparatus according to a third embodiment of the present invention; and FIG. 13 is a block diagram illustrating a water treatment control apparatus according to a fourth embodiment of the present invention. 15 DESCRIPTION OF THE EMBODIMENTS Each embodiment of the present invention will be described with reference to the accompanying drawings. FIRST EMBODIMENT 20 FIG. 1 is a block diagram illustrating a first embodiment of the present invention. In the present embodiment, an example in which a water treatment process control apparatus is applied to a standard activated sludge method is illustrated, and the water treatment process control apparatus controls a treatment of a biological reactor 10 that treats sewage by using activated sludge. The biological reactor 10 filled with the activated sludge is 25 divided into an upstream aerobic tank 11 and a downstream aerobic tank 12. From an air volume control unit 36, air is supplied to the entire biological reactor 10, namely, the upstream aerobic tank 11 and the downstream aerobic tank 12. First, influent water 1 flows in the upstream aerobic tank 11, and is treated through air and activated sludge from the air volume control unit 36. The treated influent water flows in the downstream aerobic tank 12, and is 30 further treated through air and the activated sludge fsom the air volume control unit 36. Further, the treated influent water is discharged as treated water 2 to the outside of the system. An ammonia meter (inflow) 21 being an inflow water quality estimation unit measures ammonia nitrogen concentration in influent water 1. On the basis of the measured ammonia nitrogen concentration, an upstream aerobic tank water quality target value calculation unit 3 1 calculates a target value of the ammonia nitrogen concentration in the upstream aerobic tank. On the basis of a measured value of an ammonia meter 22 as upstream aerobic tank water quality estimation unit installed at the end of the upstream aerobic tank 11 and the abovedescribed target value of the ammonia nitrogen concentration in the upstream aerobic tank, an 5 upstream aerobic tank air volume calculation unit 32 calculates an optimum air volume to be supplied to the upstream aerobic tank 11. On the basis of a flow rate of treated water 1 measured by a flow meter 20 and a measured value by an ammonia meter 22, a downstream aerobic tank water quality target value calculation unit 33 calculates a target value of dissolved oxygen concentration (DO) in the downstream aerobic tank as a target value of water quality 10 measured by a downstream aerobic tank water quality estimation unit. On the basis of the calculated target value of the DO and the measured value by a dissolved oxygen concentration meter 23 as the downstream aerobic tank water quality estimation unit installed at the end of the downstream aerobic tank, a downstream aerobic tank air volume calculation unit 34 calculates the optimum air volume to be supplied to the downstream aerobic tank 12. 15 In the present embodiment, the controllable air volume is supposed to be only the entire air volume to be supplied to the biological reactor 10 from the air volume control unit 36. Further, the upstream aerobic tank air volume and the downstream aerobic tank air volume are supposed to be uncontrollable separately. That is, on the basis of respective calculation results, a biological reactor air volume calculation unit 35 calculates the entire air volume to be supplied 20 to the biological reactor 10. A relationship between operating conditions and water quality is first obtained as a parameter peculiar to a sewage treatment plant to be controlled. In the present embodiment, a microbial reaction model typified by an activated sludge model (ASM) of International Water Association (IWA) and a flow model expressing a process of the sewage treatment plant are 25 combined and a sewage quality simulator is used. A treatment process of the sewage treatment plant to be treated by this sewage quality simulator is reproduced, and then the relationship between the operating conditions and the water quality is calculated. FIG. 2 illustrates an example of a change in the ammonia nitrogen concentration toward a flow direction. Further, FIG. 2 illustrates results of the case in which with respect to 30 different influent ammonia concentration, the ammonia nitrogen concentration of treated water is supposed to be operated by an air volume being a target value of 1 mg NIL. On the basis of the results in which the ammonia nitrogen concentration of treated water is a target value under various conditions, a relational formula of an approximated curve used for control is established. FIG. 3 illustrates a relationship between the influent ammonia concentration being water quality of influent water and target ammonia nitrogen concentration being a target value of water quality of the upstream aerobic tank. The ammonia meter 22 is installed in an aerobic tank 4 at an end of the upstream aerobic tank 11 with an aerobic tank 1 to the aerobic tank 4 being used as the upstream aerobic tank 11. It is suggested from the above drawing that in the case where water 5 quality of influent water changes with respect to the preset target value, an intermediate target value is changed to thereby obtain stable treatment. FIG. 4 illustrates a relationship between the air volume and the upstream difference water quality. Specifically, FIG. 4 illustrates a relationship between the integrated air volume required for treatment being the air volume to the upstream aerobic tank and the ammonia nitrogen concentration (an inflow value-a value of a 10 position of the ammonia meter) treated in the upstream aerobic tank 11 being a difference between water quality of the influent water and water quality of the upstream aerobic tank. It is understood that as the integrated air volume increases more, the treated ammonia nitrogen concentration increases more. FIG. 5 illustrates a relationship between the downstream difference water quality and the downstream target water quality. Specifically, FIG. 5 illustrates 15 a relationship between a target DO being a target value of water quality of the downstream aerobic tank and a load (concentration x flow rate) of the ammonia nitrogen concentration flowed into the downstream aerobic tank 12 derived from a difference between water quality of the upstream aerobic tank and target water quality of the treated water. The target DO is a DO value necessary to attain the target water quality. As a result, it is understood that as the load 20 increases more, the target DO needs to be made larger. With reference to the above relationship, the necessary air volume is determined. FIG. 6 is a flowchart illustrating an arithmetic process. At the time t=t,, an inflow flow rate Q(t,) [m3/h] is first obtained by the flow meter 20 (Step 1 : hereinafter, referred to as S 1). Next, an aeration air volume QB(t,,) [m3/h] at the present moment is obtained (S2). A calculation 25 method in the present embodiment is characterized in that a position, an aeration air volume, and ammonia treatment amount of each fluid lump flowing in the biological reactor 11 per unit time At(=t,l-t,l-l)a re calculated. A conceptual diagram of the calculation is illustrated in FIG. 7. When the fluid lump to having a cubic volume Q(to) At flows in the biological reactor 11 at the time to, a position x(to, t) at the time t of the fluid lump to is equal to a total value of the flow 30 length Q(t)/S.At (S [m2]: a cross-sectional area of the biological reactor 11 toward the flow direction) at each time (S3). In the case where the total value is more than or equal to a position X=XNH4 of the ammonia meter 22 installed at the end of the upstream aerobic tank 11, although descriptions are reversed, the inflow time at which the fluid lump gets to a position of the ammonia meter at the time t,, is to (S4). The air volume QB(t) At per unit time At with respect to - 11 - a capacity V [m3] of the biological reactor 11 acts on the capacity Q(to) At of the fluid lump in accordance with the air volume distribution function D(x) (illustrated in FIG. 8) of an average value 1 in the position x of the fluid lump. Therefore, the integrated air volume VB(to, t) [m3] with respect to the fluid lump flowing in at the time to is equal to an integrated value of an action 5 air volume QB(t)A t-Q(tO)A t/V.D(x) at each time (S5). Next, the ammonia nitrogen concentration NH4(t,,) is measured by the ammonia meter 22 installed at the end of the upstream aerobic tank 11 (S6). In the calculation of the air volume of the downstream aerobic tank, first, the downstream aerobic tank water quality target value calculation unit 33 calculates target dissolved 10 oxygen concentration DOt,(tn) on the basis of a relationship between the ammonia nitrogen concentration and FIG. 3 (S7). The downstream aerobic tank air volume calculation unit 34 calculates a downstream aerobic tank air volume QBd(fn+1S)O that the dissolved oxygen concentration DO(t,) (S8) measured by the dissolved oxygen concentration meter 23 is equal to the target dissolved oxygen concentration DOt,(t,) (S9). A PID control system is used as a 15 calculation method, and when only proportionals P are considered, the downstream aerobic tank air volume QBD(tn+,i)s represented, for example, by a (formula 1). Here, Vd [m3] denotes a capacity of the downstream aerobic tank, K [m3/hr.~/mg] denotes a proportionality constant, and a [mg/L] denotes a correction coefficient. In the case 20 where treated water is deviated from the assumed water quality (ammonia concentration) at the time of measuring the treated water by using a manual analysis, the correction coefficient a is considered to be increased and decreased. In the present embodiment, the total air volume QB is calculated on the basis of the downstream aerobic tank air volume QBd and the upstream aerobic tank air volume Qn, as described below, and therefore the downstream aerobic tank air 25 volume at the time t,, is QB(tn) Vd/V. In the calculation of the air volume of the upstream aerobic tank, first, the ammonia nitrogen concentration NH4,,,(t) of influent water at the time t is measured (S 10). The upstream aerobic tank water quality target value calculation unit 3 1 calculates the ammonia nitrogen concentration treatment amount ANH4(t,,)=NH4,,l(to)-NaHb4o(utt ,thle) fluid lump to that 30 flows in at the time to and gets to a position of the ammonia meter 22 at the time t,, (S 11). With regard to the relationship between the air volume and the upstream difference water quality illustrated in FIG. 4, the integrated flow rate VR(tOt,n ) and ANH4(t,,) are measured values of the relationship between the air volume to the fluid lump to and the upstream difference water quality, and therefore the upstream aerobic tank air volume calculation unit 32 corrects the relationship between the air volume and the upstream difference water quality by using the above measured value (S12). In the correction, a new measured point is added, and further an approximated curve may be recalculated, or a weighting factor may be changed in accordance 5 with the addition time at that moment. Next, with reference to a relationship between the influent ammonia concentration being water quality of the influent water illustrated in FIG. 3 and the target ammonia nitrogen concentration being a target value of water quality of the upstream aerobic tank (S 13), the target ammonia nitrogen concentration NH4tg(tn)b eing the target value of water quality of the upstream aerobic tank corresponding to NH4il,(tn)i s calculated (S 14). The 10 target value ANH4tg(tn)=N H4in(tn)N- H4tg(tn)o f the ammonia nitrogen concentration treatment amount is calculated on the basis of the above NH4,,(t1,). With reference to a graph about the relationship between the air volume and the upstream difference water quality corrected in S 12, the target integrated air volume VBtg(tnw) ith respect to the fluid lump t, is further calculated (S 16). 15 FIG. 9 illustrates parameters in O