What Are Two Sources Of Increased Nitrogen And Phosphorus In A River That Result From Human Activity

Biogeochemistry

K.C. Ruttenberg , in Treatise on Geochemistry (Second Edition), 2014

10.13.3.3.2.2.1 Sedimentary organic phosphorus: composition and reactivity

Organic phosphorus (P _org) is the primary vector of phosphorus delivery to marine sediments and constitutes an important fraction (~25–30%) of total P in buried in marine sediments (Colman and Holland, 2000; Faul et al., 2005; Froelich et al., 1982; Ruttenberg, 1993). Despite its importance to the total marine sedimentary phosphorus inventory, advances in understanding the compositional makeup of sedimentary organic phosphorus have been fairly limited, due in large part to the analytical difficulties associated with characterizing its molecular forms. The principle analytical challenge is that only a small fraction of sedimentary organic phosphorus can be separated into individual organic phosphorus compounds for identification and analysis; the bulk of the pool (in most cases well over 90%) is intimately associated with HMW bulk organic matter (Laarkamp, 2000) and is inaccessible to most existing analytical methodologies.

One of the most intriguing, and persistent, questions concerning the marine sedimentary organic phosphorus reservoir is the following. Given that the ultimate source of organic phosphorus to marine sediments is the phosphorus biochemicals contained within plant and animal tissues, and that these biochemicals are high-energy compounds that presumably should be labile after organism death, how is it that significant quantities of organic phosphorus persist in deeply buried (Delaney and Anderson, 1997; Filippelli and Delaney, 1996; Kraal et al., 2010a; Tamburini et al., 2003) and even in ancient (Algeo and Ingall, 2007; Ingall et al., 1993; Kraal et al., 2010b; Sandstrom, 1980; Mort et al., 2007) marine sediments? What is the mechanism by which these compounds are preserved? Persistence of organic phosphorus in deeply buried and ancient marine sediments has been explained in a number of ways, including: (1) preferential preservation of inherently refractory organic phosphorus compounds, such as phosphonates or inositol phosphates (Froelich et al., 1982; Ingall and van Cappellen, 1990; Suzumura and Kamatami, 1995), and (2) presence of bacterial biomass or derivative compounds (Froelich et al., 1982; Ingall and van Cappellen, 1990; Ruttenberg and Goñi, 1997a). Without insight into the composition of sedimentary P_org, it is not possible to conclusively determine controls on its relative reactivity or lability during early diagenesis and thus to understand preservation mechanisms.

Most information about sedimentary organic phosphorus derives from studies focusing on the size of the total P_org pool and bulk organic C:P ratios in sediments (Algeo and Ingall, 2007; Anderson et al., 2001; Filipek and Owen, 1981; Froelich et al., 1982; Ingall and Van Cappellen, 1990; Ingall et al., 1993; Krom and Berner, 1981; Morse and Cook, 1978; Reimers et al., 1996; Ruttenberg, 1993; Ruttenberg and Goñi, 1997a,b) without examining distribution among specific P_org compounds or compound classes. The size of the bulk P_org pool in marine sediments typically decreases with depth, indicating partial mineralization during early diagenesis (Cha et al., 2005; Filippelli, 2001; Filippelli and Delaney, 1996; Klump and Martens, 1987; Krom and Berner, 1981; Morse and Cook, 1978; Mort et al., 2010; Reimers et al., 1996; Ruttenberg and Berner, 1993; Ruttenberg and Goñi, 1997a; Slomp et al., 1996a; Schenau et al., 2000; van der Zee et al., 2002; see also Figure 12(a) ). Deeper in the sediments, mineralization of P_org slows to undetectable levels. The initial rapid mineralization of P_org is usually attributed to the destruction of more labile components (Ingall and Van Cappellen, 1990; Krom and Berner, 1981), and by inference, the deeply buried P_org is assumed to be more refractory. In some slow sediment accumulation rate sites, such as in the deep sea, however, sedimentary P_org concentration profiles can be invariant with depth, implying that even P_org at the sediment–water interface is refractory toward microbial mineralization (Ruttenberg, 1990). Bulk P_org concentrations alone, however, do not provide a means for explicitly supporting these inferences. Key questions include: (1) What specific P_org compounds make up the 'labile' portion of the P_org pool? (2) What is the chemical composition of the preserved, presumably refractory, P_org fraction?

Less frequently, studies have been undertaken to quantify a limited number of compounds (e.g., ATP, DNA, and phospholipids) within marine sediments (Bossard and Karl, 1986; Craven et al., 1986; Harvey et al., 1986; White et al., 1979). The relative rarity of the latter type of study is in large part because they require substantially more work than studies of the bulk P_org pool. Furthermore, the aim of such studies is usually distinct from the goal of understanding the sedimentary P_org pool in toto, but rather to understand biomass distribution or microbial activity in sediments, for which these biochemicals may serve as proxies.

Suzumura and Kamatami (1995) pursued a study of the fate of inositol phosphates in sediments, another specific class of compounds that can be isolated and quantified, with the aim of evaluating whether these terrestrial plant-derived P_org compounds might be refractory in the marine environment. Their results suggest that these compounds are minor constituents of total P_org in marine sediments, and that they are vulnerable to microbial breakdown during early diagenesis and do not persist to depth. Thus, these compounds do not provide an explanation for persistent preservation of P_org in marine sediments.

Although studies of specific P_org compounds such as these have expanded our understanding of the sedimentary P_org pool, their narrow focus on compounds, which make up at most a few percent of the total P_org pool, contribute little to our understanding of the forces driving bulk P_org trends in marine sediments.

Early work undertaken to examine the composition of the bulk sedimentary P_org pool separately quantified phosphorus associated with humic and fulvic acids in marine sediments (Nissenbaum, 1979). Results of this study suggested that P is preferentially mineralized during the diagenetic transition from fulvic to humic acid. However, because the distinction between organic and inorganic P in these fractions was not made, it is unclear whether the trends reported accurately reflect changes in P_org.

A decade after Nissenbaum's (1979) work, new advances in our understanding of the bulk sedimentary P_org pool began to be made with the application of phosphorus-31 nuclear magnetic resonance spectroscopy (³¹P-NMR) to marine sediments. ³¹P-NMR is currently the most promising tool for characterizing P_org in sediments. Application of ³¹P-NMR to the insoluble 'protokerogen' fraction of marine sediments has revealed the presence of phosphonates (Carman et al., 2000; Ingall et al., 1990; Laarkamp, 2000; Ruttenberg and Laarkamp, 2000). Phosphonates were originally viewed as promising candidates for compounds that might make up the refractory sedimentary P_org pool because their structure (a direct carbon-phosphorus bond) was thought to render them more stable than organic phosphates (Froelich et al., 1982; Ingall and Van Cappellen, 1990; Ingall et al., 1990). However, a study applying solution phase ³¹P-NMR coupled with an organic P sequential extraction method (Laarkamp, 2000) has shown that phosphonic esters are equally, if not more, vulnerable to microbial breakdown during early diagenesis than phosphate esters. Thus, the direct C–P bond in phosphonates does not appear to render these compounds more resistant to microbial respiration in marine sediments (Laarkamp, 2000; Laarkamp and Ruttenberg, 2000; Ruttenberg and Laarkamp, 2000). The nature of the 'refractory' organic phosphorus that escapes breakdown during early diagenesis, substantial quantities of which make it into the rock record, and can be quantified as P_org in ancient shales (Ingall et al., 1993; Laarkamp, 2000), thus remains an open question. Solution ³¹P-NMR can access between 10% and 60% of total sedimentary P_org (Carman et al., 2000; Ingall et al., 1990; Laarkamp, 2000) and, in addition to phosphonates, has identified phosphomono- and diesters (as well as inorganic polyphosphates) in a range of continental shelf, slope, and deep-sea sediments (Ingall et al., 1990; Laarkamp, 2000). Our understanding of what factors control the relative distributions of these different P_org compound classes is limited, but it has been suggested that sediment redox state may play a role (Carman et al., 2000).

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Phosphorus and selected metals and metalloids

Shiping Deng , in Principles and Applications of Soil Microbiology (Third Edition), 2021

Solubilization of inorganic phosphorus

Although organic phosphorus may be 30%–50% of total phosphorus in soil, inorganic forms of phosphorus are often predominant. As described earlier, inorganic phosphorus minerals such as aluminum, manganese, and iron phosphates in acidic soil and calcium phosphates in alkaline soils have low solubility in water. Orthophosphate in soil solution is supplied to the roots primarily by diffusion. Thus, chemical equilibria between orthophosphate, adsorbed orthophosphate, and inorganic phosphate minerals are important in supplying phosphorus to plants and microorganisms. As solution phosphorus is assimilated by living organisms, it is replenished from phosphorus minerals.

Some microorganisms are capable of solubilizing and converting insoluble soil phosphorus and rock phosphate to bioavailable forms. Microbial solubilization of phosphorus has long been recognized. Bacteria capable of phosphate solubilization are referred to as phosphobacteria, but the solubilizing activities are also observed among other microorganisms. Attempts have been made to isolate phosphorus-solubilizing microorganisms (PSM) for use as soil and/or seed inoculants. Examples of PSM (including bacteria, fungi, actinomycetes, and algae) are shown in Table 19.4. Phosphorus solubilizing Pseudomonas, Agrobacterium, and Bacillus are commonly isolated. Several strains of Burkholderia have also been found to be effective. For decades, Russian farmers used phosphobacterin, B. megaterium var. phosphaticum, as a bacterial inoculant. Unfortunately, the effectiveness of PSM is not consistently supported in the scientific literature. Limited success may be due, in part, to limited knowledge of the precise mechanisms by which the organisms solubilize rock phosphate and the conditions that promote solubilizing activity. It is generally accepted that mineral phosphate solubilization by PSM strains may occur due to a variety of mechanisms including lowering pH via the release of organic acids (Fig. 19.5) and producing siderophores that chelate Fe³⁺ from iron phosphate minerals. A wide range of low molecular weight acids is produced by microorganisms and plants, including inorganic acids such as carbonic acid (H₂CO₃) and organic acids such as citrate, oxalate, and gluconate. Carbonic acid can promote dissolution of calcium and magnesium phosphate compounds. The hydroxyl and carboxyl groups of the acids chelate the cations bound to phosphate (i.e., aluminum, iron, calcium, and magnesium phosphates), thereby resulting in the release of orthophosphate into the soil solution. One group of organisms that may be especially important in this regard is the mycorrhizal fungi, which form symbioses with plant roots and enhance the uptake of phosphorus and other nutrients (Chapter 12). Mycorrhizal fungi play a key role in phosphorus acquisition in the environment through forming a symbiotic relationship with the roots of nearly all vascular plants. Mycorrhizal symbioses are recognized for their importance in plant nutrition, particularly in phosphorus uptake. Under water-logged conditions, hydrogen sulfide, produced by sulfate-reducing bacteria or other processes, can also displace metal cations from insoluble phosphates, leading to the release of phosphate. The incorporation of readily mineralizable carbon sources, such as manure, can enhance phosphorus solubilization through increased biological activity. Further, the added organic carbon can complex aluminum in acidic soils, thereby reducing aluminum phosphate precipitation.

Table 19.4. Examples of phosphorus-solubilizing microorganisms (PSM) enhancing crop production.

PSM	Test crop	Result
Aspergillus niger	Wheat	Increased plant growth
Serratia sp.	Wheat	Increased plant growth
Aspergillus awamori S29	Mung bean	Increased total P content and plant biomass
Burkholderia gladioli	Sweetleaf	Increased plant growth
Pseudomonas aeruginosa	Chinese cabbage	Increased biomass production and shoot length
Pseudomonas putida	Moss	Increased plant growth
Azotobacter chroococcum, Saccharomyces cerevisiae, and Bacillus megaterium	Moringa oleifera	Increased shoot and root lengths and weights, and content of vitamin C and protein in leaves
Burkholderia gladioli	Oil palm	Increased growth and phosphate uptake
Aspergillus niger and Penicillium aculeatum	Chinese cabbage	Increased plant growth
Bacillus thuringiensis	Rice	Increased shoot length
Pseudomonas striata and Glomus fasciculatum	Soybean-wheat	Improved root development and increased grain yield
Burkholderia cepacia	Maize	Increased plant growth
Azotobacter chroococcum and Bacillus subtilis	Wheat	Improved productivity
Pseudomonas favisporus TG1R2	Soybeans	Increased dry biomass
Rhizobium tropici CIAT899	Beans	Increased nodule number and mass, shoot dry weight, and root development

Adapted from Alori et al. (2017).

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The Biosphere

William H. Schlesinger , Emily S. Bernhardt , in Biogeochemistry (Third Edition), 2013

Soil Phosphorus Cycling

Transformations of organic phosphorus in the soil are difficult to study because of the reaction of available phosphorus with various soil minerals ( Figures 4.10 and 6.19). A few workers have examined phosphorus mineralization in soils using the buried-bag approach (e.g., Pastor et al. 1984), but in many cases there is no apparent mineralization because of the immediate complexation of P with soil minerals. Thus, most studies of phosphorus cycling have followed the decay of radioactively labeled plant materials (Harrison 1982) or measured the dilution of radioactive ³²P that is applied to the soil pool as a tracer (Walbridge and Vitousek 1987, Lopez-Hernandez et al. 1998). With the isotope-dilution technique, one must assume that ³²P equilibrates with all the chemical pools in the soil and that the only dilution of its concentration is by the mineralization of organic phosphorus (Kellogg et al. 2006). Unfortunately, these assumptions are not always valid, making the technique difficult to apply in many instances (Walbridge and Vitousek 1987, Di et al. 1997, Bunemann et al. 2007).

In the face of difficulty measuring P mineralization directly, many workers have used sequential extractions to quantify phosphorus availability in the soil (Hedley et al. 1982b, Stevenson 1986, Tiessen et al. 1984). Extraction with 0.5 M NaHCO₃ is a convenient index of labile inorganic and soluble organic phosphorus in many soils (Olsen et al. 1954, Sharpley et al. 1987). Organic P is often determined as the difference between PO₄ in a sample that has been combusted at high temperatures and an untreated sample (Stevenson 1986); microbial P, by the change in extractable phosphorus after fumigation with chloroform (Brookes et al. 1982, 1984).

Extraction with NaOH (to raise pH and lower anion adsorption capacity) indicates the amount of P that is held on Fe and Al minerals, while extraction with HCl releases P from many Ca-bound forms, including CaCO₃ (Tiessen et al. 1984, Cross and Schlesinger 1995). Acid-extractable phosphorus also includes P derived from apatite (Chapter 4), including secondary hydroxyapatite—Ca₅OH(PO₄)₃—from bones and fluoroapatite—Ca₅F(PO₄)₃—in teeth. These biominerals in soils are sometimes used by archeologists to determine the location of past human activity and settlements (Sjöberg 1976, Vitousek et al. 2004).

In most ecosystems, much of the phosphorus available for biogeochemical cycling is held in organic forms (Chapin et al. 1978, Wood et al. 1984, Yanai 1992, Gressel et al. 1996), especially inositol phosphates (Turner and Millward 2002). These organic forms can be isolated and identified using phosphorus-31 nuclear magnetic resonance spectroscopy (Turner et al. 2007, Turner and Engelbrecht 2011). Earlier we discussed the ability of soil microbes, mycorrhizae, and plant roots to release phosphatase enzymes and organic acids that mineralize P from organic and inorganic forms (see also Chapter 4).

Much of the P in decomposing materials is found in ester linkages (i.e., -C-O-P). These groups may be mineralized by the release of extracellular enzymes (e.g., phosphatases) in response to specific microbial demand for P (McGill and Cole 1981). Release of acid phosphatases by soil microbes is directly related to levels of soil organic matter (Tabatabai and Dick 1979, Polglase et al. 1992). During forest development, the phosphorus taken up from labile pools in the soil is replenished by P released from the anion adsorption and nonoccluded pools, which presumably equilibrate with the soil solution over longer periods (Richter et al. 2006).

Walbridge et al. (1991) found that up to 35% of the organic P in the undecomposed litter in a warm-temperate forest was held in microbial biomass, and Gallardo and Schlesinger (1994) found that additions of inorganic P increased the microbial biomass in the lower horizons of a forest soil in North Carolina, where the mineralogy is dominated by Fe and Al-oxide minerals with strong phosphorus adsorption capacity. Similar results are reported for tropical forests (Cleveland et al. 2002, Liu et al. 2012). P immobilization in microbial biomass also dominated P cycling in some European grasslands (Banemann et al. 2012). In the course of decomposition, organic phosphorus compounds move from the forest floor to the lower soil profile, where they accumulate in humus (Schoenau and Bettany 1987, Qualls and Haines 1991, Kaiser et al. 2003, Turner and Haygarth 2000).

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Analytical Methods for Total DOM Pools

Jonathan H. Sharp , in Biogeochemistry of Marine Dissolved Organic Matter, 2002

A. HISTORICAL PERSPECTIVE AND THE ANALYTICAL PROBLEM

Some estimates of organic phosphorus in seawater were made from the 1930s on by various wet chemical methods. Probably the first seawater routine methods to measure total dissolved phosphorus (TDP) were the UV ( Armstrong et al, 1966) and the persulfate (Menzel and Corwin, 1965) methods. A routine HTC method for dried samples was suggested as an alternative (Solorzano and Sharp, 1980b). A critical step in this HTC method that could cause poor recovery if omitted is the acid hydrolysis to cleave any polyphosphates formed in drying the sample. One reason for introducing the HTC method was that the UV method was shown to give incomplete recovery of specific organic phosphorus compounds. A second reason was that the HTC method was very simple and easily performed on large numbers of samples without any special equipment.

All of the DOP methods appear to be similar in basic principle (Fig. 6). A water sample is treated to convert all organic phosphorus compounds to DIP, also called orthophosphate. Unlike with the numerous nitrogen species, there is only one oxidation state in the DIP. Actually due to dissociation of the phosphoric acid, there are three ions but all are measured as the same under the acid conditions of the colorimetric method. The DOP concentration is determined after conversion by subtracting the DIP from the TDP. Most organic phosphorus compounds contain a phosphate ester bond linking the orthophosphate molecule to an organic molecule which is broken to free the orthophosphate. Checks with specific organophosphorus compounds indicated incomplete recovery of compounds like ATP by the UV method, suggesting that some of the ester bonds may be difficult to break without complete destruction of the organic molecules (Solorzano and Sharp, 1980b). It should be noted that all DOP methods, similar to DON methods, require pre- and postmeasurement of DIP. Thus, the error for DOP analysis is compounded and the accuracy of DOP measurements is weakened if DIP measurements are not accurate.

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Phosphorus Cycle☆

Y. Liu , J. Chen , in Encyclopedia of Ecology (Second Edition), 2014

Food Consumption and Human Wastes

The third source of organic phosphorus available, in principle, for cropland is human waste. Assuming the world human body mass averaging 45 kg per capita (reflecting a higher proportion of children in the total population of low-income countries) and phosphorus content in human body averaging 470 g P per capita implies a global anthropomass contains approximately 3.0 MMT P. The typical daily consumption is about 1500 mg P per capita for adults (CEEP, 1997). This is well above the dietary reference intake (DRI), the amount human individual should take each day, as recommended by the Food and Nutrition Board, Institute of Medicine, US National Academy of Science. The US-recommended intakes are 700 mg per capita for adults over 18 years of age, 1250 mg per capita for young adults between 9 and 18 years of age, and 500 mg per capita for children.

A similar estimate for China is derived from a previous study: the individual daily intake of phosphorus was 1400 mg P per capita for urban residents and 1470 mg P per capita for rural residents in 2000. This exceeds the DRI of 1000 mg per capita recommended by the Chinese Nutrient Society. In addition, livestock products provided 30% of daily phosphorus intake for Chinese urban residents and 14% of that for rural population.

According to total protein intake and percentage of protein from vegetable sources, the mass phosphorus produced from human wastes annually on a capita basis in combined urine and feces ranges from 0.18 to 0.73 kg in 2009. Human excreta and urine contained about 3.4 and 1.7 MMT P year^{− 1}, respectively. Urban and rural population generated 2.7 and 2.4 MMT P year^{− 1}, respectively (Mihelcic et al., 2011).

Application of human excreta as organic fertilizer is common both in Asia and in Europe, but less prevalent elsewhere in the world. The nutrient linkage between farmers and croplands has been relatively stable, but the human wastes in urban areas are less recycled than in rural areas. For instance, less than 30% of human wastes in urban areas were recycled for agricultural uses in the late 1990s in China. This percentage dramatically decreased from 90% in 1980. In contrast, about 94% of human wastes in rural areas were returned to croplands in the 1990s. In European countries, the recycling rate of urban sewage averaged about 50% over the 1990s. Globally, it could be appropriate to assume that about 20% of urban human wastes and about 70% of rural human wastes are recycled at present. Therefore, recycled human wastes amount to 2.2 MMT P year^{− 1}.

Adding the quantities of the phosphorus recycled as crop residues, animal manures, and human wastes, the total organic fertilizers applied to croplands amount to 6.4 MMT P year^{− 1}. This is equivalent to 24% of the applied amount of inorganic fertilizers. Thus, the global input of phosphorus to croplands is probably 26.2 MMT P year^{− 1} in total or 1.9 times the amount of the phosphorus removed from the soil by harvesting. This leads to a net accumulation of 12.3 MMT P year^{− 1} or 7.9 kg P ha^{− 1} in global soils, disregarding erosion and runoff losses.

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Lakes and fjords of Polar regions—potential indicators of climate change

Shabnam Choudhary , ... Neloy Khare , in Understanding Present and Past Arctic Environments, 2021

3.3.2 Organic components (TOC, TN, and TP)

Organic element proxies such as organic carbon, nitrogen, and phosphorus are indicators of the status of past productivity. C/N ratio is a widely used indicator of the source of the organic matter and helps to understand the biogeochemistry of the environment. Depth-wise distribution of the organic elements is presented in Fig. 3.5. In core LA, TOC showed lower than the average values in the lower depths range from 26 to 20 cm and higher than the average values in the upper portion from 8 to 6 cm and at 2 cm with an overall increasing trend toward the surface (Fig. 3.5A). TN and TP showed uniform distribution throughout the core. C/N ratio fluctuated around the average line up to a depth of 6 cm, and further, it showed lower than the average values suggesting the source of organic matter to be autochthonous.

In core K-1, TOC fluctuated around the average line throughout the core. TOC showed negative peaks at depth 22 and 4 cm similar to that of silt and clay, respectively, and a positive peak at 15 cm similar to that of silt indicating that these sediment components regulated the distribution of organic matter at these depths. Further, TOC showed an increasing trend from 4 cm to the surface similar to that of clay toward the surface, suggesting increased primary productivity. Fluctuating trend with depth indicates changing rate of supply of organic matter through changing processes (Choudhary, 2019). Organic matter concentration in the sediments of fjord mainly depends on the location of sampling. Whether the sampling location lies in the proximity of high primary production areas or the glaciers are available in the vicinity, supplying land-derived material. The high concentration of land-derived material causes high turbidity resulting in the shallow photic zone. Regions receiving a high amount of freshwater discharge from glaciers and rivers fed by glaciers, generally, have low primary production due to the high turbidity (Gorlich et al., 1987; Zajączkowski and Włodarska-Kowalczuk, 2007). The marine organic matter gets diluted with suspended material discharged by glaciers. Therefore glaciers play an important role in regulating the distribution of organic matter in the fjord system. TN and TP showed higher concentration in the lower depth range from 23 to 17 cm and an increasing trend toward the surface in the upper portion. TN showed a positive peak at 14 cm similar to that of clay and TP at 9 cm similar to that of TOC. TN does not show similarity with TOC in its distribution throughout the core indicating their different source.

C/N ratio of core K-1 varied from 5.60 to 84.03 (average 28.52) indicating a mixed source of organic matter derived from marine as well as terrestrial. C/N ratio showed lower than average values in the lower depth range from 23 to 14 cm while at 13 cm C/N ratio was found to be high (Fig. 3.5B), similar to that of sand indicating ice-free conditions and increased glacial meltwater, which must have delivered terrestrial organic matter to the fjord. The high primary production may lead to nitrogen limitation in the surface water. Also, the nitrogen loss in sediments can be possible due to diagenesis, which must have resulted in a relatively large range of C/N ratio. Further, it decreased up to 4 cm and then increased toward the surface.

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Immobilized Cells

I. Wojnowska-Baryła , ... E. Klimiuk , in Progress in Biotechnology, 1996

Introduction

A biological process for the combined removal of organic matter, nitrogen and phosphorus from waste water using activated sludge has been studied and applied at the full scale [1], [2]. Major factors limiting this process depend on the composition of influent waste water and biomass concentration in tanks. The process has been developed to allow suspended biological growth, therefore the required retention time should be about 14 hours. This means that in order to achieve a satisfactory level of nitrogen and phosphorus as well as BOD removal from waste water it is necessary to develop the system with a higher rate of biomass accumulation. Nowadays immobilization by adsorption is mainly applied for this purpose [3]. In that way pure cultures are immobilized [4]. In this investigation the immobilization of mixed cultures by inclusion in two types of carrier was applied.

This paper describes the results of an experimental study on removal of phosphorus and nitrogen from waste water by immobilized activated sludge with the ability to store orthophosphate intracellularly.

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PHOSPHORUS

I.D. McKelvie , A. Lyddy-Meaney , in Encyclopedia of Analytical Science (Second Edition), 2005

Photochemical Methods

Ultraviolet (UV) photooxidation may be employed to convert organic phosphorus to phosphate prior to detection, and can be performed either in batch mode using a high-intensity, ventilated UV source and a quartz reactor vessel, or in continuous-flow mode using either quartz or polytetrafluoroethylene (PTFE) photoreactors. Because batch UV radiation systems usually involve the use of high wattage UV lamps (e.g., 1000 W) and extended irradiation times, condensed phosphates are hydrolyzed due to the elevated temperature and gradual acidification of the sample as peroxydisulfate degrades to form sulfuric acid. Thus, UV photooxidation alone is insufficient to convert condensed phosphates to orthophosphate, and the use of UV photooxidation with alkaline peroxydisulfate may provide a basis for discrimination between the organic and condensed phosphorus fractions.

Photooxidation of organic phosphorus may be performed by UV irradiation on the untreated sample, and relying on the dissolved oxygen present in the sample to provide an adequate source of oxygen or hydroxyl radicals. However, it is more common that hydrogen peroxide, peroxydisulfate, ozone, or other oxidizing agents are added to enhance the completeness of the oxidation process.

When H₂O₂ is exposed to UV light, it forms hydroxyl radicals:

$H_{2} O_{2} + h ν \to 2 {OH}^{•}$

This radical is among the strongest oxidizing agents found in aqueous systems and initiates a series of radical chain reactions with organic substances, resulting in mineralization of the sample to bicarbonate and orthophosphate.

Photooxidation using peroxydisulfate also produces hydroxyl radicals and oxygen by the following route:

$S_{2} O_{8}^{2 -} + h υ \to 2 {SO}_{4}^{•}$

${SO}_{4}^{•} + H_{2} O \to {HSO}^{4 -} + {OH}^{•}$

$S_{2} O_{8}^{2 -} + {OH}^{•} \to {HSO}^{4 -} + {SO}_{4}^{•} + \frac{1}{2} O_{2}$

${SO}_{4}^{•} + {OH}^{•} \to {HSO}_{4}^{-} + \frac{1}{2} O_{2}$

Titanium dioxide-mediated oxidation of organic phosphorus can also be achieved using long-wavelength UV. Excitation of an electron from the valence band (v) into the conduction band (c) creates an electron–hole pair, which may then react with, for example, oxygen adsorbed to the TiO₂ surface to produce radicals such as $O_{2}^{-}$ and ${OH}^{•}$ .

In order to determine the TP concentration in water, the digestion process must involve both oxidative and hydrolytic processes in order to hydrolyze P–O–P linkages (e.g., polyphosphates) and oxidize phosphoesters and C–P compounds to inorganic phosphate. For example, in an online TP digestion system, which involves both thermal digestion and UV photooxidation, it is necessary to use a mixture of sulfuric acid and peroxydisulfate in order to obtain high recoveries of both organic and condensed phosphorus.

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Wastewater Treatment and Reuse

S. Sengupta , in Comprehensive Water Quality and Purification, 2014

3.1.4.1.5 Biological phosphorus removal

Phosphorus is found in the aquatic environment in several forms including organic phosphorus, water soluble inorganic, and insoluble inorganic forms of phosphorus. Of these different forms, the water soluble inorganic form is the most important because it can be consumed by phytoplankton directly and contributes to surface water productivity directly. Phosphorus is an important nutrient, especially in oligotrophic environment. Surface water productivity in terms of phytoplankton and other plants depends on the external as well as internal sources of phosphorus. To control eutrophication, more emphasis is put on decreasing the inputs of phosphorus in freshwater lakes. It has been understood that phosphorous is the limiting nutrient in lakes and estuaries.

Biological phosphorus removal is accomplished through a process commonly known as enhanced biological phosphorus removal (EBPR), as discussed in Chapter 3.9. EBPR has developed and advanced over the past 50 years, and activated sludge plants operating completely on the enhanced biological phosphorus removal process are now found worldwide (Seviour et al., 2003). In an EBPR-activated sludge plant, the influent wastewater sequentially flows through an anaerobic and aerobic zone, after being mixed with the returned activated sludge from the clarifier to form the mixed liquor. The cycling of the microbial biomass along with the influent wastewater through anaerobic and aerobic zones brings about a selection of microorganisms having a high capacity to accumulate polyphosphate intracellularly in the aerobic period. This group of bacteria is known as polyphosphate-accumulating organisms (PAOs). When PAOs grow, they not only consume phosphorus for their cellular growth and maintenance but also accumulate large quantities of orthophosphate in the form of polyphosphate within their cells. This accumulation is known as the 'luxury uptake.' The biomass is then separated from the treated water at the end of the process through sludge wastage, and net phosphorus removal is achieved (Grady et al., 1999). Chapter 3.9 discusses in detail the EBPR microbiology, the existing models for anaerobic and aerobic EBPR metabolisms, how various configurations of the activated sludge reactor can be designed to accomplish EBPR, and what factors affect EBPR.

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Estuarine and Coastal Ecosystem Modelling

G. Arhonditsis , ... W. Zhang , in Treatise on Estuarine and Coastal Science, 2011

9.10.3.1.6 Phosphorus cycle

Two state variables of the phosphorus cycle are considered in the model: phosphate (PO₄) and OP ( Figure 5 ). The phosphate equation considers the phytoplankton uptake, the proportion of phytoplankton and zooplankton mortality/higher predation that is directly supplied into the system in inorganic form, the bacteria-mediated mineralization of OP, and the net diffusive fluxes between epilimnion and hypolimnion. We also accounted for the phosphorus precipitation to sediment due to the iron loadings from the two steel mills, based on an empirical equation originally implemented to correct for the observed Hamilton Harbour phosphorus concentrations (Hamilton Harbour Technical Team – Water Quality, 2007). The OP equation also considers the amount of OP that is redistributed through phytoplankton and zooplankton basal metabolism. A fraction of OP settles to the sediment and another fraction is mineralized to phosphate through a first-order reaction. We also consider external phosphorus loads to the system and losses via the exchanges with Lake Ontario.

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https://www.sciencedirect.com/science/article/pii/B9780123747112009104