Which of the following is a measure of the degree of acidity or alkalinity of the urine?

4.3 Determination of acidity/alkalinity and pH

Acidity/alkalinity and pH are among the most common and relevant analytical measurements made in industrial processes and laboratories. The flow analysis concepts have been applied to facilitate this measurement directly through the use of potentiometric [45,46] and spectrophotometric detection [47,48]. Alternatively, the acidity can be determined by flow-based (FIA, SIA) pseudo-titration based on concentration gradients produced by dispersion [49–51] or by means of true flow titration [15,52,53]. The concept of true titration, in the present context, is associated with the use of only one standard (titrant) solution of known concentration and stoichiometry of the titration reaction to calculate the analyte concentration.

The use of FIA and SIA systems for pH measurements using pH sensors allow for reproducible sampling operation and automatic sample dilution and ionic strength adjustment. The calibration made by using standard buffer solutions is also carried out in flow systems, resulting in a high sample throughput (>120 samples h−1) and high precision (typical, 0.1 pH units). Because the sample is washed out by the carrier solution, the sensor is maintained under a stable condition contributing for its performance and durability.

The pseudo-titration in FIA systems can be used to determine acidity and alkalinity. However, it possesses a clear drawback in terms of process analysis: the necessity of calibration standards and frequent recalibration to correct flow rate variations. On the other hand, the system is fast and can provide almost real-time results for process control.

A new approach to flow titration based on flow rate ratio has been described in which the principle of compensating errors is applied to avoid the lag time between the compositional change and its detection [54]. The system, when applied to a process stream with slow change in concentration of acid or base can reach unbeatable speed (3 s per titration), reproducibility (0.2–0.6% RSD) and titrant volume consumption (12 μL per titration). However, the system is based on flow rate ratios between titrant and sample streams and this is a source of weakness in the system.

The adaptation of a true titration to the MSFA concept has also been demonstrated recently [55]. The analyser exploited in full the FB hybrid characteristic of the MSFA and the titration can be conducted in accordance with the IUPAC definition for titration. The sample volume (40–100 μL), titrant concentration and reaction stoichiometry are the only parameters needed for determination of acidity/alkalinity. A possible drawback of this type of flow titrator is in the relative long time necessary to perform a titration (2–5 min).

Specific applications of flow systems for off-line determination of acidity and acid content in samples of industrial interest include the use of a monosegmented system for total acidity in vinegar [56], acidity in metallurgical solutions using MSFIA [57], total acidity in silage extract using MCFIA [58], total acidity in soft drinks and fruit juices using pseudo-titration in a SIA system [49,59], and, recently, a FIA pseudo-titration performed in non-aqueous media for the determination of free fatty acids in samples of palm oil [50].

6.2.2 By-products from wastewater

First and foremost, contaminants in wastewaters are extremely suspended solids, COD, heavy metals, color, turbidity, alkalinity, acidity, and other soluble substances (Amoah et al., 2020; IWA, 2018; Jayaswal et al., 2018). These contaminants, when discharged to the water bodies without treatment, pose serious ecological problems (Amoah et al., 2020; Hsien et al., 2019). For instance, textile industries are water intense and use approximately 21–377 m3 of water per ton of textile produced (Kant, 2012; Nigam et al., 1996; Wang et al., 2011). Many industries use dyes expansively for several operations, such as textile, paper, plastic, leather, and tanning. (Salgot and Folch, 2018; Tetteh and Rathilal, 2020a,b). There are different types of pollutants that migrate from the dyeing to the finishing processes of textile industries. In fact, upon reclamation of water from wastewater for reuse, the pollutant loads are usually reduced to certain levels without affecting the quality. However, there are undesirable health and environmental influences associated with water pollution (Kant, 2012; Nigam et al., 1996; Wang et al., 2011).

Wastewater treatment routes generate a wide-ranging amount of by-products, which mostly depend on the initial concentration of the organic compounds and chemical usage (Cruz-Salomón et al., 2019; Gerba and Pepper, 2019; Mohapatra and Kirpalani, 2019; Salgot and Folch, 2018). A chunk of these by-products originates from the coagulation/flocculation and the biological treatment processes contributing to chemical sludge and activated sludge, respectively (Daud et al., 2018; Gerba and Pepper, 2019; Musa et al., 2018). However, both types of sludges preceding the filtration process can be separated by a settler or clarifier or DAF units (Tetteh and Rathilal, 2020a,b; Angelakis and Snyder, 2015; Deng and Zhao, 2015; Gao et al., 2014; Kelly and He, 2014). Conventionally, the goal of most of these WWTPs is to separate the pollutants from water (treated water) and dispose of the accumulated pollutants in solid waste to landfills without considering its value. Currently, there are a lot of research works, studies, rules, regulations, etc., on how to manage these by-products (Angelakis and Snyder, 2015; Van Der Hoek et al., 2016; Van Lier et al., 2015). Furthermore, a centralized wastewater treatment management system can be used to recover most of the resources and nutrients, and some are presented in Table 6.5.

Table 6.5. Resource recovery from wastewater distribution systems (Angelakis and Snyder, 2015; Safoniuk, 2004; Van Der Hoek et al., 2016).

6.2.3 Analytical Methods

Immediately after sampling, unfiltered samples were measured for pH (Orion 5–Star BENCHTOP MULTI, Thermo Scientific, USA), acidity, and alkalinity (APHA-AWWA-WEF, 2005). Filtered (0.2 µm cellulose nitrate membrane, Whatman GmbH, Dassel, Germany) samples were immediately analyzed for SO42− (discussed in Chapter 5: Reactivation of Reactor and Role of Supplement and Neutralizing Substances), acidity, alkalinity, chemical oxygen demand (COD) (spectrophotometric), dissolved sulfide (titrimetric) (APHA-AWWA-WEF, 2005), and acetate (HPLC method discussed in this chapter).

24.5 Application of Microcapsules in Graphic and Paper Industry

There are many reasons as to why microcapsules are used in variety of applications. Some of them are isolation/protection of material from surrounding influences (e.g., heat, oxidation, acidity, alkalinity, and moisture) and from interacting with other compounds in the system, which may result in degradation or polymerization, inhibiting evaporation of volatile material (e.g., perfumes, essential oils, and volatile flavors during baking), masking materials with unpleasant flavors or smell, improved handling of material with microcapsules (e.g., sticky materials), and finally also protecting workers or end users from exposure to hazardous substances (Nelson, 2001), converting liquid-active components into a dry solid system, and so on.

In graphic industry, microcapsules with different shell and different functional core materials have been used over the years. They have been applied to various products such as coating, impregnation, and interlayer. Some interesting applications are listed in the continuation.

Looking into the history of graphics, the first successful commercial use of pressure-ruptured microcapsules was conducted by Green and Schleicher. In the year 1945, coating for paper or similar web-like material was patented (Green, 1945). This coating was described as rupturable, elastic, solid film having dispersed profusely and random, minute marking-liquid-containing cells of the so-called low polarity or oil type, which are not affected adversely by atmospheric conditions causing hydrolysis, drying, or oxidation. Upon applied localized pressure, coating would release included liquids, which would mark the surface upon which the coating is overlaid. Carbonless copy paper, which is composed of several sheets of paper, as shown in Figure 24.7, was patented in 1957 (Green, 1957; Green & Schleicher, 1957). The backside of the top paper is covered with the layer of microencapsulated ink. The shell of these microcapsules ruptures when the pressure of pencil/printer is applied. Released ink (leuco/diazo dyes) reacts with the reactive clay layer on the lower paper, thus producing on it very accurate trace of ink and the same on the next sheet.

Carbonless copy paper was, according to the Technical Association of the Pulp and Paper Industry (TAPPI), one of the most important paper-related innovations of the past half-century. In the following years, many improvements on this application were made (Bakan et al., 1962; Brynko, 1961; Macaulay, 1962). In these applications, ink was incorporated in microcapsules; however, it must be noted that microcapsules can also be incorporated into ink (e.g., thermally expandable microcapsules or fragranced microcapsules as described in continuation).

Thermally expandable microcapsules, composed of a wall and the core material, which is a liquid expanding agent, such as a low boiling hydrocarbon or other volatile material, were used in different inventions. During the core vaporization at elevated temperature, the pressure inside these microcapsules increases and expands the wall by several times. Later, it was suggested (Morehouse & Tetreault, 1971) to use these microcapsules in fabrication of laminates (with improved heat insulation), where expandable microcapsules would be presented in the middle of two sheets of the paper. Expandable microcapsules are included also in low-density paperboard articles (Mohan et al., 2005), paper, and paperboards with reduced tendency to cut, abrade, or damage human skin (Williams et al., 2005), printing inks for raised prints (Figure 24.8) (Urbas et al., 2014), and so on. Expandable microcapsules are also used in the reproduction of braille dots or tactile images. Raised prints are made with thermo pen, which due to its higher temperature initiates chemical reaction—expansion of microcapsules on capsulated (e.g., swell) paper. Expansion degree of polystyrene core material depends on temperature—the higher the temperature, the higher the degree of expansion.

In 1966, an interesting application on paper with incorporated hollow microcapsules was patented (Kenaga & Gooch, 1966). They made improvements on weight of conventional paper by incorporating hollow microcapsules with polymethyl methacrylate shell. By this invention, they were able to get paper with lower density, improved opacity and stiffness per unit weight, and lower thermal conductivity.

In 1991, the process of wetting a paper web in a calendering step by using water-containing microcapsules was patented (Korpela, 1991). Those microcapsules were composed of water in core and water-impermeable shell, which was ruptured in the calendering step, and thus water was released. Microcapsules with water or a hydrated salt in the core were also used in other patent (Geer, 1977). It was suggested that those microcapsules are incorporated in a paper sheet, which is further subjected to the electrostatographic fusing operation where water was released from the microcapsules to replenish that lost due to the heat of fusing. Thus, paper can be imaged on its other side without encountering the problems associated with dehydration of the paper.

Microcapsules with a variety of uses include fragranced microcapsules. Among them is “scratch and sniff” application enabled with the development of appropriate shell composed of urea–formaldehyde polymer in early 1970s (Matson, 1970) and later melamine–formaldehyde polymer. It was suggested in a patent (applied by Matson, 1970) that these microcapsules are particularly adapted for their incorporation either as coatings on or as inclusions within papers and other sheet materials. After that patent, a lot of applications were proposed in the field of “scratch and sniff” technology. In 1971, a teaching book with fragrance microcapsules was included into prints for establishing an association between selected stimuli of the chemical senses and identifications, which was patented (Ladd & Emerson, 1971). In 1981, scratch and smell puzzles were patented (Spector, 1981). On playing board, pictures of different smelling objects were printed, while pressure-ruptured fragrant microcapsules were included in ink. In 1985, a new usage of fragrance-releasing microcapsules printed on a transparent label was patented (Sweeny, 1985). Usage of this patent was intended as art overlays, scented transferable tattoo, and so on (Stanislav, 1998). Other applications of fragranced microcapsules are also fragrance-releasing insert for a magazine, air freshener card, publicity inserts, unwoven paper tissues, aromatherapeutic articles made with paper substrates printed or impregnated with microcapsules, and so on. However, perfume-containing microcapsules can also be incorporated into aqueous printing inks and applied on various substrates by different printing techniques (e.g., screen printing (Urbas et al., 2014)).

Besides the above mentioned, various applications are known with different types of microcapsules such as photosensitive and electronic-ink microcapsules, phototriggerable microcapsules for chemical delivery, for printed electronics (in electrophoretic displays), in bioactive paper, and so on.

Let us end this chapter with Van Parys (Ghosh, 2006) conclusion: “The range of applications is limited only by the imagination.”

Overview of the History of pH Measurement

pH is the abbreviation for Latin “pondus hydrogenii”; pondus stands for power, and hydrogenii stands for hydrogen. In chemistry, the pH scale is a numeric index used to specify acidity and alkalinity of aqueous solutions. The pH value is calculated from the negative log of hydrogen-ion concentration in aqueous solution, which is a very important measure in vast application areas, including but not limited to chemistry, human biology, oceanography, steel industry, and agriculture. The history of pH measurement can be traced back to the fact that people began to realize that different food have distinct taste. In early time, people believe that food tasted sour belonged to the category of acids and the bitter taste food was classified as bases. Others similar to sodium chloride were classified as a kind of salt.

It has been a long time that people were using their own sense of taste to distinguish acids and bases, especially for farmers who directly taste land soil and judge the acidic or basic conditions, which causes many diseases. Thanks to Robert Boyle, the famous British physicist and chemist, who accidentally discovered a very useful indicator, litmus, to distinguish acids and bases in 1648. Boyle observed that the color of gillyflowers changed into red when exposed in hydrochloride acid and returned into its initial blue color in basic solutions. Based on his observation, Boyle invented the very first pH test strip, which has been widely used in the next four centuries. Even today, this brilliant invention is still in common use in modern laboratories. The measurement is very simple and low cost, a drop of test solution was dropped onto the pH test strip, a distinct color change was observed, and the pH value can be read via comparison with the standard color card. This outstanding invention ends up the long history of judging acid and bases using our own taste buds and opens the gate for monitoring acidity and alkalinity using artificial tools. Since its first invention, pH test stripe becomes the most widely used analytic tool in all kinds of applications. However, the accuracy of the method is not very high, and pH test stripe should not be wetted by water before used.

The modern definition of pH value was initiated by the Danish chemist Søren Peder Lauritz Sørensen, who was the first person to relate pH values to the concentration of hydrogen ions and introduced the concept of pH in 1909 [1]. He then revised the concept into modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. pH, as a simple expression of the acidity and alkalinity of solution, is a function of hydrogen-ion concentration and water dissociation:

H+ OH−H2O=KH2O=1×10−14

pH is calculated as the negative logarithm value of hydrogen-ion concentration:

pH=−lgH+

Usually, pH value ranges from 0 to 14. However, the pH value of a solution can also be < 0, which indicates that the concentration of hydrogen ions in solution is already > 1 mol/L. It is more convenient to use the concentration of hydrogen ions directly. Pure water can decompose into the same amount of hydrogen ions and hydroxyl ions:

H2O→H++OH−

The concentration of these ions is equivalent to 10− 14 mol/L:

H+OH−=10−14

In neutral solutions, the concentration of hydrogen ions is 10− 7, and the pH value of the solutions is equivalent to 7. Solutions with a pH < 7 are acidic, and solutions with a pH > 7 are basic. Pure water is neutral, at pH 7 (at 298 K), being neither an acid nor a base.

With the discovery of acid-base indicators, pH value can be simply measured in the way of titration with the aid of these pH indicators. The end point of titration is indicated by color change of the acid-base indicator. This approach is still widely in use in chemistry practical course in university laboratories, but is not commonly used in other applications, which simply because the method is hardly leading to the invention of instrumentation. Modern laboratories and test facilities are equipped with many simple, compact, and even handheld devices, called pH meter or conductance meters.

The very first commercial pH meter was designed by Arnold Beckman in around 1936. His pH meter composes all components of modern devices, including a glass electrode, a reference cell, and an electrometer [2,3]. The pH meter builds up a small voltage difference between the ion-selective electrode and the reference electrode, and pH value can be deduced from the voltage reading according to the calibration curve [4]. Because of its compact size, simplicity of use, and low cost of fabrication, pH meter is still the most widely used and reliable device for measuring pH values. However, this device still has several shortcomings, including the need of constant calibration, since it cannot give reproducible electromagnetic field over longer periods of measuring. Its fragile structure and slow response lead to long measurement time and poor reproducibility [5–8]. The measurement requires large sample volume, and the size of the glass electrode is simply too big to measure pH inside cells [9,10]. Although needle-type pH electrode has been invented for intracellular pH measuring [11], its size is still large compared with the size of a cell, and inserting the electrode into a single cell always requires specific technique and, at the same time, causes physical damage to cell membrane.

The introduction of nuclear magnetic resonance (NMR) provides a noninvasive and nondestructive approach for imaging intracellular pH. This approach relies on the measurement of concentration ratio of protonated and deprotonated forms of phosphate groups, which is a function of pH and allows for simple calculation of intracellular pH. Intracellular molecules, such as ATP and ADP, can act as intrinsic reporters, and no other reagent is needed for pH measuring. The first measurement of pH using 31P NMR was conducted by Moon and Richards in red blood cells in 1973 [12]. Since then, 31P NMR becomes a method of choice in measuring pH value in cytoplasm and cell fluid according to chemical shifts. However, the instrumentation for NMR is rather bulky, complex, and expensive. In addition, the technique suffers from its low sensitivity, and high concentration of cells or long data acquisition time is required.

In contrast to the aforementioned sensors, optical pH sensors, especially fluorescence-based sensors, have received wide attention during the last decades because of good flexibility, compact size (in nanometer range), requirement of small sensing volume, tunable sensitivity and measurement range [13,14]. More importantly, the method is capable to measure the distribution of pH inside cells, which can achieve a high-throughput imaging for statistical analysis.

8.02.4.1 Chemical Machining

Chemical machining (CHM) causes serious environmental problems due to the use and disposal of various hazardous chemicals such as cleaning solutions, etchants, and strippers. In addition, the cost associated with their handling and disposal are very high. The chemicals also have damaging effects on different materials through acidic corrosion. The etchants used in CHM change the level of acidity and alkalinity, which affects the flora and fauna in soil and water. Aquatic life faces a survival challenge if the pH level of normal water changes due to pollution. Corrosive gases can be generated in chemical machining from the aerosols of solid (nitrogen and sulfuric oxides) or liquid corrosive substances. These gases could be a source of environmental pollution, including water and soil, due to the formation of acid when combined with water.

Among several health effects, irritation; corrosive injuries and burns; rapid, severe, and often irreversible damage of the eyes; and larynx and lung cancer are frequently reported in chemical machining. Properties of the substance, the concentration, and time of contact with acids and alkalis are the determining factors for health-related problems.

A current industrial trend is to select more environmentally friendly chemicals. Moreover, studies have been carried out on regeneration of waste etchant and etched metal recovery from waste etchants (92). It was found that a suitable regeneration/recovery system could be developed for some etchants like FeCl3, CuCl2, and alkaline etchants. Wearing personal protective equipment is recommended to avoid any contact with the hazardous chemicals.

1 Introduction to the Anatomy and Physiology of the Bladder

The bladder is a hollow, very complex, semi-spherical organ that consists of multiple layers. The largest area of the bladder efficiently accumulates, stores, and releases urine produced by the kidneys, as directed by the central nervous system [1–4]. The bladder's anatomical structure is described as being complex because of the presence of multiple, diverse layers, including the urothelium (the innermost layer), the lamina propria, the longitudinal muscle layer, and the circular muscle layer (on the outer end), as shown in Fig. 1 [2,5].

7.2.2.3 Alkalinity Generation

The pH values of the effluents were in the alkaline range (Fig. 7.3) from the start of flow continuation. The pH got below 7 in both columns after 90 days of operation. During this period, SMC was able to counter the acidity of AMD. The jar test result (Table 7.1) showed that it could produce near 1000 mg/L alkalinity (as CaCO3 equivalent) in seven days, countering acidic water. With normal water, the alkalinity was near 1600 mg/L. After 105 and 141 days of operation for the coal and metal mine water, respectively, the pH of the effluents dropped below 5.5. Effluent acidity and alkalinity concentrations were 203 and 87 mg/L, and 213 and 65 mg/L, correspondingly. It was the stage where the SMC was exhausted in terms of alkalinity generation. At this point, NaHCO3 was added as a buffering agent into the reservoirs, and influent pH was maintained close to 6. It is well known that SRB works well in the pH range of 5–9. At this stage, it was not obvious to add alkalinity from outside in ideal circumstances, especially when acid production is not a mechanism in the ongoing reactor. However, sulfate reduction in the SMW media generally takes place in the acidogenic phase (see Chapter 4: Dosing with Product from the Waste: Use of Fractions). Low pH in this phase essentially lessened the sulfidogenesis efficiency. After two to three weeks of NaHCO3 addition, the effluent pH increased to 7 again. The values were steady at 7.2 to 7.3 and near 8 for the coal and metal mine water treating columns, respectively. In contrast to influent pH of 6, the higher effluent pH confirms bicarbonate alkalinity production by microbial sulfate reduction. Effluent alkalinity values were 205 to 300 mg/L in this phase.

Materials containing treated straw produce high alkalinity when dissolved (Koschorreck et al., 2002). Ground chalk is generally present in SMC of Indian origin, which produces extra alkalinity. The SMC in the columns could produce sustained alkalinity over 200 mg/L when the pH of the effluents was over 5.5. Suffice to say that produced alkalinity was a combination of the SMC liberated fraction and the microbial sulfate reduction mechanism. The cessation of microbial sulfate reduction rate resulted in lower bicarbonate alkalinity generation. Liberation of alkalinity from the SMC also declined. The addition of SMW into the reactor initiated the acidogenesis. Produced acid, therefore, could not be neutralized by system-generated alkalinity. Hence, the pH reduced sharply. Supply of bicarbonate alkalinity from outside countered the acidity; hence, the performance in the reactors became stabilized again.

3.1.6.3 Water Sampling and Analysis

Water samples were collected at 3 and 4 day intervals from the static and continuous flow experiments, respectively. All samples, except for TSS analysis, were filtered through a 0.45 µm nylon membrane filter to remove precipitates and other solid materials (Younger and Wolkersdorfer, 2004). Metal concentrations were quantified by atomic absorption spectrophotometry (GBC 932, Australia) after pretreatment with 1.5 µL of concentrated HNO3 per mL sample (Clesceri et al., 1998). Sulfate measurement was carried out using the turbidometric method (Csuros, 1997) with a 420 nm spectrophotometer (Ocean Optics Inc. SD 2000). Acidity, alkalinity, and TSS were determined by standard methods (Clesceri et al., 1998). Oxidation reduction potential (ORP), pH, DO, conductivity, total dissolved solids (TDS), and salinity were measured with a multi-parameter water analyzer (Orion 5-Star BENCHTOP MULTI, Thermo Scientific, USA). Total organic carbon (TOC) was measured with a TOC analyzer (TOC-VCPH, Shimadzu, Japan) using the filtered sample, and was reported as dissolved organic carbon (DOC) (Khan et al., 1998). The water used for all of the analyses had a resistivity between 16 and 18 mega ohm-cm. Whenever possible, the pH, acidity/ alkalinity, DO, TDS, TSS, conductivity, salinity, and sulfate were determined on the same day the samples were collected. Glassware and plastic-ware used in this study were cleaned by soaking in 10% nitric acid, rinsing several times with Milli-Q water, and finally oven drying.

Influent (sample port in tank D) and effluent (tank F) water were collected at seven day intervals regularly. Metal and sulfate concentrations, pH, ORP, and DOC were analyzed by the same methods discussed earlier. Limestone exhaustion in terms of calcium ion concentration was measured before and after the experiment. Total bacterial count of the reactor matrix was performed by the standard plate count method on trypticase soy agar. The SRB count of the matrix was done by the most probable number (MPN) method described by Fortin et al. (2000). Reactor matrix was taken during sampling, weighed and diluted into respected dilution before plating or MPN experiment. Total bacterial population is expressed in CFU/g matrix, whereas SRB population is expressed in MPN/g matrix. An epifluorescence microscopic method was used for observing bacterial morphology and live−dead differentiation (Leica DMR coupled with Leica MPS60 photomicrographic system). In brief, 1 g of matrix was homogenized in 100 mL 1X PBS buffer. One and half milliliters was centrifuged at 5000 rpm for 3 min, and the supernatant was discarded. The pellet was dissolved in 1 mL PBS buffer and again centrifuged under similar conditions. Acridine orange (AO) and propidium iodide (PI) of 2 μL each were added to the pellet, and the volume was adjusted to 25 μL by 1X PBS buffer. The tubes were then incubated for 20 min in the dark. After incubation, the stains were washed three times with PBS buffer, and then centrifuged for 4 min at 5000 rpm to pellet the cells. The pellet was dissolved again in PBS buffer to make the volume 500 μL. Living bacteria would produce green fluorescence (due to AO), and dead would produce red.

Suppression of Indigenous Nonhydrogen-Producing Bacteria

Although biohydrogen can be obtained from a variety of organic solid wastes, hydrogen production was often deteriorated by indigenous microorganisms. Organic solid wastes itself can be an unwanted inoculum source because they have many kinds of hydrogen-consuming bacteria and nonhydrogen-producing acidogens (Li and Fang, 2007). Therefore, in order to enhance hydrogen production, organic solid wastes require pretreatment to suppress the activities of the undesirable organisms, such as methanogens, homoacetogens, and lactic acid bacteria. In principle, hydrogen-producing bacteria such as Clostridium are physiologically different from nonhydrogen-producing bacteria (Das and Veziroglu, 2001). Clostridium can form protective spores under harsh conditions such as high temperature, extreme acidity, and alkalinity, whereas methanogens cannot. Thus, researchers have applied several pasteurizing methods for eliminating or suppressing the activity of nonhydrogen-producing bacteria from organic solid wastes, as shown in Table 4.

Table 4. Pasteurizing Methods for Eliminating or Suppressing the Activity of Nonhydrogen-Producing Bacteria

Thermal pretreatment has been widely used to facilitate the suppression of nonspore-forming bacteria. Noike et al. (2002) found that continuous hydrogen production from bean curd manufacturing waste was impossible due to the existence of lactic acid bacteria in the substrate, but could be overcome by heat treatment of the feedstock at 50–90°C for 30 min. Similarly, a study on hydrogen production from a mixture of food waste and sewage sludge also reported that heat treatment of feedstock (100°C, 10 min) was effective in eliminating methanogenic activity in a semicontinuous flow reactor (Zhu et al., 2011). Hydrogen from food waste without inoculum addition is also feasible. Kim et al. (2009) demonstrated that food waste successfully served not only as a substrate, but also as a source of hydrogen-producing bacteria when heat (90°C for 20 min), acid (pH 1.0 for 1 day), or alkali (pH 13.0 for 1 day) treatment was applied. These pretreatment methods inhibited lactate production and increased hydrogen and butyrate production. Among three pretreatments, heat treatment showed the highest hydrogen yield (97 ml-H2/g-VS), followed by acid treatment (90 ml-H2/g-VS) and alkali treatment (51 ml-H2/g-VS).

However, a low temperature could repress lactic bacteria activity. Jo et al. (2007) observed shifts in the microbial community from Clostridium spp. to Lactobacillus spp. within a food waste-fed anaerobic reactor, which resulted in the conversion of hydrogen fermentation to lactic acid fermentation. It was found that the substrate competition between hydrogen producers and nonhydrogen producers caused an instability of continuous hydrogen production. However, when the feed solution storage tank was controlled at a low temperature (4°C), significant shifts in the microbial community did not occur and hydrogen production was maintained stably.

Most methanogens are neutrophilic with a narrow pH range of 6–8, while hydrogen-producing bacteria can grow over a relatively broad pH range. Acid/base treatments are thus efficient to repress methanogenic activity and to allow growth of spore-forming bacteria. Kim and Shin (2008) investigated the effects of acid and base pretreatments on the reduction of indigenous bacteria in food waste and the microbial population in hydrogen fermentation. They observed that base pretreatment reduced indigenous anaerobic bacteria in food waste by 4.9 log and enabled stable long-term operation over 90 days with a hydrogen yield of 62.6 ml-H2/g-VS, whereas acid pretreatment of the feedstock showed no positive effect on hydrogen production.