Orthophosphate Concentrations Research Articles

Theoretical equilibrium lead(II) solubility revisited: Open source code and practical relationships.

A theoretical equilibrium lead(II) (Pb(II)) solubility model coded in Fortran (LEADSOL) was updated and implemented in open source R code, verified against LEADSOL output, and used to simulate theoretical equilibrium total soluble Pb(II) (TOTSOLPb) concentrations under a variety of practical scenarios. The developed R code file (app.R) is publicly available for download at GitHub (https://github.com/USEPA/TELSS) along with instructions to run the R code locally, allowing the user to explore Pb(II) solubility by selecting desired simulation conditions (e.g., water quality, equilibrium constants, and Pb(II) solids to consider). In addition, the R code serves as a reproducible baseline for alternative model development and future model improvements, allowing users to update, modify, and share the R code to meet their needs. Using the R code, several solubility diagrams were generated to highlight practical relationships related to TOTSOLPb concentrations, including the impact of pH and dissolved inorganic carbon, orthophosphate, sulfate, and chloride concentrations.

Recovery of phosphorus as soluble phosphates from aqueous solutions using chitosan hydrogel sorbents

This manuscript presents new method of phosphorus recovery from aqueous solutions in a convenient form of readily-soluble phosphates using chitosan hydrogels. Non-modified chitosan hydrogel granules (CHs) and chitosan hydrogel granules crosslinked with epichlorohydrin (CHs-ECH) served as orthophosphate ion carriers. The developed method was based on cyclic sorption/desorption of orthophosphates, with desorption performed in each cycle to the same solution (the concentrate). The concentrations of orthophosphates obtained in the concentrates depended on, i.a., sorbent type, sorption pH, source solution concentration, and desorption pH. Phosphorus concentrations in the concentrates were even 30 times higher than these in the source solutions. The maximum concentrate concentrations reached 332.0 mg P-PO4/L for CHs and 971.6 mg P-PO4/L for CHs-ECH. The experimental series with CHs-ECH were characterized by higher concentrations of the obtained concentrate, however the concentrates were also more contaminated with Cl− and Na+ ions compared to series with CHs. The high content of chlorine and sodium ions in the concentrates was also favored by the low pH of sorption (pH < 4) and very high pH of desorption (pH > 12) in the cycles. After concentrate evaporation, phosphorus content in the sediment ranged from 17.81 to 19.83% for CHs and from 16.04 to 17.74% for CHs-ECH.

Effective orthophosphate removal from surface water using hydrogen-oxidizing bacteria: Moving towards applicability

Effective orthophosphate removal strategies are needed to counteract eutrophication and guarantee water quality. Previously, we established that hydrogen-oxidizing bacteria (HOB) have the ability to remove orthophosphate from artificial surface water. In the present study, we expand the application of the HOB orthophosphate removal strategy (1) to treat artificial surface water with low initial orthophosphate concentrations, (2) to treat real surface water and real wastewater effluent, and (3) to remove orthophosphate continuously. For synthetic surface water, irrespective of the initial concentration of 0.7, 0.5, 0.3, and 0.1 mg PO43−-P/L, ultra-low concentrations (0.0058 ± 0.0028 mg PO43−-P/L) were obtained. When artificial surface water was replaced by real surface water, without added nutrients or other chemicals, it was shown that over 90% orthophosphate could be removed within 30 min of operation in a batch configuration (0.031 ± 0.023 mg PO43−-P/L). In continuous operation, orthophosphate removal from surface water left an average concentration of 0.040 ± 0.036 for 60 days, and the lowest orthophosphate concentration measured was 0.013 mg PO43−/L. Simultaneously, nitrate was continuously removed for 60 days below 0.1 mg/L. The ability to remove orthophosphate even under nitrogen limiting conditions might be related to the ability of HOB to fix nitrogen. This study brings valuable insights into the potential use of HOB biofilms for nutrient remediation and recovery.

Can Ephemeroptera, Plecoptera, Trichoptera (EPT) assemblage reflect nitrogen and phosphorus load in the riverine ecosystem?

The aim of this paper is to make a comparative analysis of benthic macroinvertebrate compositions in streams and rivers in Croatia with relation to different physical-chemical factors, especially nutrients. Samples were collected according to the AQEM method. At all the sites, 20 taxa were recorded of which Turbellaria, Gastropoda, Bivalvia, Oligochaeta, Hirudinea, Crustacea, Ephemeroptera, Odonata, Plecoptera, Heteroptera, Trichoptera, Coleoptera and Diptera were included in the present study. Water temperature mostly affected the composition of benthic macroinvertebrates to which it was inversely proportional. Nutrient enrichment, i.e., higher concentrations of ammonium, nitrates, nitrites, total nitrogen, orthophosphates and total phosphorus mostly affected Ephemeroptera, Plecoptera, Trichoptera and Diptera, by decreasing their diversity.

Tidal and Physicochemical Effects on Phytoplankton Community Variability at Tagus Estuary (Portugal)

The Tagus Estuary is one of the largest estuaries in Europe and merges large urban and industrial areas. Understanding phytoplankton community variability is key for an appropriate assessment of the estuarine ecological status. The objective of the present study was to assess the importance of the tidal influence over the phytoplankton community and to evaluate its main drivers of variation. Weekly sampling was performed at two stations on the Tagus Estuary with different anthropogenic pressures (Alcântara and Barreiro). The sampling covered periods with different tidal amplitude. Alcântara presented both the lowest and highest concentrations of dissolved inorganic nitrogen (DIN) and orthophosphate concentration (DIP), depending on the tidal height. Such high variability in this sampling station is probably due to its proximity to a sewage treatment station outfall and to the estuary mouth. In the present study, both seasonal and tidal variations influenced the chlorophyll a concentration of which the tidal cycle explained up to 50% of the chlorophyll a variations. Chlorophyll a displayed a seasonal trend with two peaks of phytoplankton biomass between spring and mid-summer. The main drivers of chlorophyll a variation were radiation, water temperature, tidal amplitude, salinity, river discharge, and the inorganic nutrients DIN and DSi. The estuarine phytoplankton community was mainly dominated by Bacillariophyceae, especially at Alcântara. Bacillariophyceae were less important at Barreiro, where communities had a higher representation from other phytoplankton groups, such as Cryptophyceae and Prasinophyceae. The drivers of variability in the community composition were similar to those influencing the total biomass. In conclusion, the spring-neap tidal cycle strongly influenced the phytoplankton community, both in terms of biomass and community composition. Of the several tidal conditions, spring tides were the tidal condition that presented both higher biomass and higher Bacillariophyceae representativity in the community.

Rotifers in the Niger River, Niger: diversity and abundance in relation to environmental parameters

A first study of the rotifers of the Niger River in Niger is reported here. Two surveys took place under contrasting hydrological conditions: low-water level (16 April to 8 May 2018) and high-water level (1 to 15 February 2019). Zooplankton and physico-chemical parameters were sampled at eight stations spread over 520 km from Ayorou to Gaya. In total, 32 taxa were identified, including 26 at species level. During the low-water sampling, Polyarthra sp. (31%), Brachionus caudatus (23%), Synchaeta longipes (11%), Keratella tropica (7%) and Filinia longiseta (5%) were the most abundant, whereas Brachionus quadridentatu s (26%), Lecane hastata (25%), Keratella cochlearis (9%), Keratella lunaris (5%), Hexarthra sp. (3%) were dominant during the high-water sampling. The mean abundance of rotifers ranged between 14 × 103 ind. m−3 during the high-water sampling and 244 × 103 ind. m−3 during the low-water sampling. The highest diversity was observed in the three stations located upstream from the city of Niamey. The results reflect the difference in environmental parameters between the downstream and upstream Niamey stations. RDA analyses showed that the main environmental factors explaining the distribution of rotifers were dissolved oxygen, orthophosphate and nitrate concentrations.

Assessing rainwater quality treated via a green roof system

The shortage of water worldwide is increasingly worrying. Studies in the field suggest that sustainable water resource management via water recycling is fundamental to alleviate the issue. The use of rainwater is an important alternative source that must be considered, mainly, in the water crisis facing the planet. When integrated with the concept of green roofs, the capturing and treatment of rainwater in these structures becomes an even more ecological and sustainable practice. The water drained by the roof can be used for non-potable uses, such as flushing toilet bowls. One of the main concerns when using rainwater, even for non-potable uses, is the quality of the water available, so as not to put users' health at risk. In this way, the present work proposes to experimentally analyze the quality of rainwater drained in a green roof prototype for reuse purposes. The green roof prototype was installed on an experimental bench. After each rain event (four in total), two water samples were collected in the following situations: rainwater captured directly by a container next to the bench and rainwater, drained by the green roof prototype, captured by a container through existing drains at the base of the prototype. The analyses of the collected samples were carried out at the Environmental Engineering Laboratory (LEMA/UFRJ) and performed according to the Standard Methods for the Examination of Water and Wastewater. Specifically, the experiments examine physicochemical and biological parameters following a rain event on a green roof prototype for sanitary use. Experimental results that were observed and analyzed include color, turbidity, pH, ammonia nitrogen, nitrite, nitrate, orthophosphate, total coliforms, and thermotolerant coliforms to indicate the rainwater quality from green roofs. The majority of parameters assessed were within the value thresholds indicated by the Brazilian standards, while the results of orthophosphate, fecal coliforms, color, and turbidity were not. The greatest divergence is in the concentration of orthophosphate, where a concentration of 10.88 mg/L was obtained in this experimental study, while other authors present values of 0.1 and 0.01 mg/L. Total coliforms also presented high values, but within the expected range. Comparisons with technical documents and international references related to water quality to identify possibilities of the use of rainwater were also conducted. Results indicate that the water quality has the same order of quantity for turbidity, nitrite, and ammonia nitrogen parameters across the standards. Based on such observations, filtration and disinfection processes are therefore required in the green roof system for the use of rainwater for sanitary. Finally, the experimental study of rainwater quality on the green roof presented similar results comparing with international references. The use of green roofs combined with the use of rainwater demonstrates the potential and benefits as an alternative to face the water crisis.

Performance of constructed wetland for selenium, nutrient and heavy metals removal from mine effluents

Passive biological treatment using constructed wetlands has been employed as a cost-effective and environmentally friendly alternative for mine effluents treatment in Canada. The current work aimed to assess the performance of a laboratory-scale constructed wetland for the removal of selenium, nutrients and heavy metals. This work achieved a maximum selenium removal rate of 54.13% corresponding to the highest hydraulic residence time (almost 47 days). Typha Latifolia was efficient for selenium assimilation and removal from mine effluent. 4.4% of Se mass was accumulated in the under and aboveground biomass while 32.2% was volatilized. Levels <1.69 mg of selenate, <1.69 mg of selenite, <3.39 mg of selenomethionine and <3.39 mg of unknown selenium species were distributed in the underground biomass while levels <0.75 mg of selenate, <0.75 mg of selenite, <1.51 mg of selenomethionine and <1.51 mg of unknown selenium species were found in T. Latifolia leaves. Ammonia removal was mainly based on a nitrification process confirmed by the decrease of ammonia (>96%) and nitrite in association with the increase of nitrate concentrations in the outlet compared to the inlet. The concentrations of other nitrogen compounds mainly thiocyanate and cyanate have significantly decreased from initial average values of 163 and 22.7 mg.L−1 in the influent to 1.5 and 0.3 mg.L−1 final concentrations, respectively. Orthophosphate concentrations were also efficiently decreased from an influent average value of 21.5 ± 3.3 mg.L−1 to an effluent concentration of 9.1 ± 4.4 mg.L−1. Understanding the selenium and nutrient removal mechanisms will allow treatment performance enhancement and the development of large-scale constructed wetlands for sophisticated mine effluent treatment.

Long-term response in nutrient load from commercial forest management operations in a mountainous watershed

An increased emphasis on fuel management strategies to mitigate wildfire risks is raising the awareness and need for comprehensive forest management strategies that satisfy long-term water quantity and water quality needs. Forest management activities can alter the soil nutrient pools and affect the timing and magnitude of stream water quantity and quality. We investigated the effect of contemporary forest management activities, including clear-cutting and thinning, on water yield and stream nitrogen and phosphorus dynamics in a quarter-century-long (1992–2016) paired and nested watershed study in the interior Pacific Northwest, US. Monthly water samples were collected and analyzed for total Kjeldhal nitrogen (TKN), total available nitrogen (TAN), nitrate + nitrite (NO3 + NO2), total phosphorus (TP), and orthophosphate (OP) concentrations throughout the study period. Five years of pre-disturbance data, 4 years of post-road construction, 6 years of Phase I (PH-I) experimental post-harvest, and 9 years of Phase II (PH-II) operational harvest data were analyzed using a before-after, control-impact paired series (BACIPS) study design. We found statistically significant increases in stream NO3 + NO2 loading from the paired and nested watersheds following timber harvest treatments. In the case of OP, any increase in nutrient load was attributed to increases in streamflow, as OP concentrations remained near minimum detectable concentrations. Streamflow increased the greatest following clear-cut practices (33.4% at W1 during PH-I) with the largest response in stream NO3 + NO2 concentration (up to 0.33 mg-N L−1 at W1). In-stream NO3 + NO2 and OP concentrations were lower in the downstream cumulative watersheds, which was likely due to dilution and nutrient assimilation effects. Interestingly, the NO3 + NO2 concentration, streamflow, and loads of NO3 + NO2 and OP from the undisturbed control watershed also increased. This increase was, however, smaller than the harvested watersheds and likely driven by climate variability or subtle forest succession changes. In summary, we found that contemporary forest management activities increased stream NO3 + NO2 concentrations and loads following timber harvest activities, but these effects were also attenuated due to downstream uptake processes. Furthermore, relative to post-wildfire impacts, these nutrient increases are small and short-lived.

Response of the rearing water bacterial community to the beneficial microalga Nannochloropsis oculata cocultured with Pacific white shrimp (Litopenaeus vannamei)

As a greenwater technology, coculturing microalgae with shrimp can improve the rearing water microenvironment and optimize aquaculture sustainability. However, little is known about the extent to which rearing water bacterial communities can be regulated by coculturing and how it occurs. Here, using 16S rRNA gene amplicon sequencing, we investigated the assembly of the bacterial community in a shrimp rearing system cocultured with Nannochloropsis oculata. Lower nutrient concentrations were detected in the N. oculata cocultivation system. Furthermore, a significant regulatory effect of N. oculata cocultivation on the bacterial community structure was also observed. Specifically, N. oculata cocultivation enriched the bacteria affiliated with the orders Flavobacteriales, Desulfuromonadales, Rhizobiales and Rhodobacterales but depleted some opportunistic pathogens such as Vibrionales, Sphingobacteriales and Xanthomonadales. Estimation of the β-nearest taxon index (βNIT) indicated that N. oculata cocultivation could drive the bacterial community assembly from stochastic processes to deterministic processes, and these deterministic effects were attributed to the concentrations of orthophosphate and ammonium (explained 24% of community variation) and the microalgae (explained of 12% community variation) through canonical correlation analysis (CCA) and variance partitioning analysis (VPA). Additionally, network analysis revealed that N. oculata cocultivation could also remodel the co-occurrence patterns and niche characteristics in bacterial community. By linking the modules with nutrient factors, two bacteria affiliated with the genus Psychroserpens and the and order Rhizobiales were negatively correlated with nitrate and orthophosphate, thereby identified as functional bacteria that might cooperate with N. oculata to remove nutrients. Our findings about the assembly processes and co-occurrence patterns of rearing water bacterial community will contribute to understanding and developing greenwater technology for improving rearing water quality.

Effects of carbohydrate addition methods on Pacific white shrimp (Litopenaeus vannamei)

The addition of external carbohydrate in Pacific white shrimp (Litopenaeus vannamei) culture has shown positive effects on water quality and shrimp performance. However, this practice requires additional skills and labor, and therefore may not be widely adopted. This research investigated the potential to combine the carbon source and the feed in one pellet in shrimp culture. The carbon source used in this experiment was corn starch. The experiment was executed in 6 indoors mesocosms tanks, with full control of the water source, temperature, and light intensity and duration. The three treatments including COM-Feed (commercial feed), COM-Feed + CHO (commercial feed with separate corn starch addition), and CHO-Feed (pelleted diet made by incorporating additional corn starch into the commercial feed) were randomly assigned to the mesocosms tanks, and run two times consecutively. Adding corn starch separately resulted in higher shrimp biomass gain and protein efficiency ratio (P < 0.05), compared to dietary corn starch addition and no corn starch addition. Carbohydrate addition caused a significant drop in inorganic nitrogen and orthophosphate concentrations in the water. The treatments had no effect on the biofloc and periphyton growth, and the proximate composition of shrimp, biofloc, and periphyton, however increased the eukaryotic microbial diversity in the bioflocs. Meanwhile, the carbohydrate addition reduced the dietary energy and carbon utilization efficiencies regardless of the carbohydrate addition methods.

A Simple and Accurate Approach for Determining the VFA Concentration in Anaerobic Digestion Liquors, Relying on Two Titration Points and an External Inorganic Carbon Analysis

A new analytic approach is presented for determining the total volatile fatty acids (VFAT) concentration in anaerobic digesters. The approach relies on external determination of the inorganic carbon concentration (CT) in the analyzed solution, along with two strong-acid titration points. The CT concentration can be determined by either a direct analysis (e.g., by using a TOC device) or by estimating it from the recorded partial pressure of CO2(g) in the biogas (often a routine analysis in anaerobic digesters). The titration is carried out to pH 5.25 and then to pH 4.25. The two titration results are plugged into an alkalinity-mass-based equation and then the two terms are subtracted from each other to yield an equation in which VFAT is the sole unknown (since CT is known and the effect of the total orthophosphate and ammonia concentrations is shown to be small at this pH range). The development of the algorithm and its verification on four anaerobic reactor liquors is presented, on both the raw water and on acetic acid-spiked samples. The results show the method to be both accurate (up to 2.5% of the expected value for VFAT/Alkalinity &gt;0.2) and repetitive when the total orthophosphate and ammonia concentrations are known, and fairly accurate (±5% for VFAT &gt;5 mM) when these are completely neglected. PHREEQC-assisted computation of CT from the knowledge of the partial pressure of CO2(g) in the biogas (and pH, EC and temperature in the liquor) resulted in a very good estimation of the CT value (±3%), indicating that this technique is adequate for the purpose of determining VFAT for alarming operators in case of process deterioration and imminent failure.

The Pulse of the Amazon: Fluxes of Dissolved Organic Carbon, Nutrients, and Ions From the World's Largest River

AbstractThe Amazon River drains a diverse tropical landscape greater than 6 million km2, culminating in the world's largest export of freshwater and dissolved constituents to the ocean. Here, we present dissolved organic carbon (DOC), organic and inorganic nitrogen (DON, DIN), orthophosphate (PO43−), and major and trace ion concentrations and fluxes from the Amazon River using 26 samples collected over three annual hydrographs. Concentrations and fluxes were predominantly controlled by the annual wet season flood pulse. Average DOC, DON, DIN, and PO43− fluxes (±1 s.d.) were 25.5 (±1.0), 1.14 (±0.05), 0.82 (±0.03), and 0.063 (±0.003) Tg yr−1, respectively. Chromophoric dissolved organic matter absorption (at 350 nm) was strongly correlated with DOC concentrations, resulting in a flux of 74.8 × 106 m−2 yr−1. DOC and DON concentrations positively correlated with discharge while nitrate + nitrite concentrations negatively correlated, suggesting mobilization and dilution responses, respectively. Ammonium, PO43−, and silica concentrations displayed chemostatic responses to discharge. Major and trace ion concentrations displayed clockwise hysteresis (except for chloride, sodium, and rubidium) and exhibited either dilution or chemostatic responses. The sources of weathered cations also displayed seasonality, with the highest proportion of carbonate‐ and silicate‐derived cations occurring during peak and baseflow, respectively. Finally, our seasonally resolved weathering model resulted in an average CO2 consumption yield of (3.55 ± 0.11) × 105 mol CO2 km−2 yr−1. These results represent an updated and temporally refined quantification of dissolved fluxes that highlight the strong seasonality of export from the world's largest river and set a robust baseline against which to gauge future change.

Water quality in the ecosystem of sea cucumber Acaudina sp. in the Delta Wulan Waters, Central of Java, Indonesia

Sea cucumber Acaudina sp. is one of the benthic animals which has a very important role for the benthic ecosystem in a waters. One of its roles is to maintain sediment stability and is also known as a bioturbation animal. The research aims are to study the water quality in the ecosystem of sea cucumber in the Delta Wulan Waters, Demak. The research was conducted for 4 months (May, June, July and August 2020). Based on the research result, the type of substrate in the Delta Wulan Waters is silt has a range 87.4–96.70%. The salinity has a range value is 29.25 to 33.50 ppt. The value of the water temperature is 28.6–29.9 °C. The DO value has a range is 5.04–8.13 ppm. The pH value range is 6.05–7.–56. Furthermore, the average concentration of Pb in sediment has range 4.775.10 mg/kg. The average concentration of Cu in sediment has range 15.93–16.06 mg/kg. The average concentration of Cd in sediment has range 0.02–0.07 mg/kg. In the sediment, the average concentration of ortho-phosphate content has range 0.014–0.027 mg/g, nitrate has range 0.035–0.073 mg/g and chlorophyll-a has range 268-805 mg/m2. In conclusion, water quality in Delta Wulan Waters can still support population growth of Acaudina sp..

Invasion of floating fern alters freshwater macroinvertebrate community structure with implications for bottom-up processes

The non-native aquatic fern giant salvinia, Salvinia molesta Mitchell (Salviniaceae), poses a risk to freshwater ecosystems through limiting light penetration, decreasing submerged aquatic vegetation (SAV) abundance, altering water quality, and potentially leading to changes in macroinvertebrate community structure. Here, we conducted repeated quarterly field surveys and measured light, nutrients, water quality, and aquatic macroinvertebrate community composition and energetic value to detect effects from giant salvinia invasion. Giant salvinia reduced dissolved oxygen, pH and light availability in the aquatic environment, and increased the concentration of orthophosphate and ammonium. Following initial colonization, macroinvertebrate communities in giant salvinia resembled SAV communities dominated by aquatic insects, however, richness and relative abundance in giant salvinia decreased over time, resulting in a community populated by few taxa, primarily crustaceans. Total macroinvertebrate energetic value in giant salvinia was significantly lower than SAV communities. Giant salvinia invasion changed habitat composition, triggered internal nutrient loading, and reduced macroinvertebrate abundance, diversity, and ecosystem productivity. Our findings demonstrate larger ecological impacts from giant salvinia than previously reported, including potential disruption to the transfer of energy between trophic levels.

Influence of Abiotic Factors on the Growth of Cyanobacteria Isolated from Nakdong River, South Korea1.

Changes in physico-chemical factors due to natural climate variability and eutrophication could affect the cyanobacterial growth patterns in aquatic systems that may cause environmental health problems. Based on morphological and 16S rRNA gene analysis, three cyanobacterial species isolated for the first time from the Nakdong River water sample in South Korea were identified as Amazoninema brasiliense, Microcystis elabens, and Nododsilinea nodulosa. The variations in temperature, pH, nitrogen, or phosphorus levels significantly impacted the cyanobacterial growth patterns. The optimal temperature range for the growth of isolates was from 25-30°C. A neutral or weak alkaline environment favored growth; however, A. brasiliense resulted in 44.2-87.5% higher biomass (0.75g·L-1 as dry solids, DS) and growth rate (0.24·d-1 ) at pH 7 than the other isolates (0.4-0.52gDS·L-1 , 0.16-0.19·d-1 ). The increased nitrate-nitrogen (NO3 -N) concentrations significantly (P<0.05) favored biomass production and growth rate for A. brasiliense and M. elabens, respectively, andthe maximum growth rate was observed for A.brasiliense at 3.5mgNO3 -N·L-1 . The orthophosphate concentration (PO4 -P) from 0.1 to 0.5mgPO4 -P·L-1 increased the growth of the isolates. These observations suggest that isolate growth rates in water bodies can vary depending on different physico-chemical parameters. This study contributes to the further understanding of the growth of microalgae in natural freshwater bodies under fluctuating environmental conditions and aquatic ecosystem stability.

A comparative study on biogas production, energy balance, and nutrients conversion with inter-stage hydrothermal treatment of sewage sludge

As an alternative to pre-stage hydrothermal treatment (HT) before anaerobic digestion (AD), inter-stage HT (i.e., AD-HT-AD) has been proposed to increase biogas production and to further reduce the residual organic matter. The goal of this study was to evaluate the effect of inter-stage HT at 155 °C on the ultimate biodegradability and AD extent of sewage sludge mixture (i.e., primary and waste activated sludge). The sludge ultimate biodegradability was evaluated through biochemical methane potential tests. AD-AD and AD-HT-AD configurations were investigated in semi-continuously fed bench-scale digesters in terms of methane production, solids reduction, nutrients transformation, and energy balance. Results were compared with those of AD and HT-AD configurations from our previous study. Inter-stage HT increased the ultimate biodegradability of the sludge mixture; however, pre- and inter-stage HT resulted in comparable overall specific methane production. Compared to AD and HT-AD, AD-AD and AD-HT-AD had comparable methane production, higher VS destruction (by 3.4–9.3%), but lower overall crude protein removal (by 4.0–7.5%) and soluble orthophosphate concentration decrease (by 32.5–60.8%). There was minimal difference in net energy production by AD and AD-AD (single digester vs. two digesters; 1.4 GJ/d), as well as by HT-AD and AD-HT-AD (pre-HT vs. inter-HT; 0.4 GJ/d). High HT heat recovery is needed for HT-AD and AD-HT-AD to obtain energy balance comparable to AD and AD-AD. Compared to single-step AD, the two-step AD process is more complex and thus less attractive for the digestion of sewage sludge with a relatively high ultimate biodegradability as was the case in this study. However, AD-HT-AD may be more beneficial considering post-AD sludge handling processes.

Accumulation and Release of Arsenic from Cast Iron: Impact of Initial Arsenic and Orthophosphate Concentrations

Various iron oxyhydroxide and oxide minerals commonly found in old cast iron pipe scale were shown to exhibit high and similar affinity for arsenate [As(V)] and orthophosphate (PO4) via adsorption, co-precipitation, and other factors. PO4 is a common drinking water corrosion inhibitor. This 7.5-year study examined the accumulation and release of As from an old cast iron pipe scale by changing initial As(V) (0, 75, or 180 µg/L as As) and initial PO4 (0 or 3 mg/L as PO4) levels in the simulated drinking water. The results showed that sites within the iron scale accumulated As with a large capacity and concentrated 27% of the total amount As in water into the scale during the 7.5-year study. When no PO4 was added, the As accumulation followed a linear regression model with an accumulation rate of 0.27/hr (R2 = 0.80, p < 0.001), and higher initial As level of 180 µg/L (vs 75 µg/L) resulted in 2.3-3 times larger As accumulation rate at 0.25 mg/day (vs 0.084-0.11 mg/day). As much as 44 µg/L As was released back to water following the changes in the initial As and PO4 concentrations in water. Addition of 3 mg/L PO4 caused a rapid increase in As release from iron scale that gradually dropped off with time while PO4 was incorporated into the scale and most PO4 remained tightly bound to certain iron scale sites. Proactive measures such as sampling for As in the distribution systems following PO4 corrosion control treatment changes would help identify exposure risks.

Effect of Phosphorus Application on Arsenic Species Accumulation and Co-Deposition of Polyphenols in Rice Grain: Phyto and Food Safety Evaluation.

The present study was aimed at exploring the effect of soil application of different concentrations of orthophosphate (P) (0, 10, 20, 30, and 40 mg kg−1) on rice agronomic and yield parameters, arsenic (As) species accumulation, and polyphenol levels in the grain of rice grown under As spiked soil (10 mg kg−1). The contents of As species (As(V), As (III), MMA and DMA) and polyphenols in rice grain samples were estimated using LC-ICP-MS and LC-MS/MS, respectively. P treatments significantly reduced the toxic effects of As on agronomic parameters such as root weight and length, shoot and spike length, straw, and grain yield. Among the treatments studied, only the treatment of 30 mg kg−1 P helps to decrease the elevated levels of As (V), As (III), and DMA in rice grains due to As application. The study revealed that 30 mg kg−1 was the optimal P application amount to minimize AS accumulation in rice grains and As-linked toxicity on agronomic parameters and chlorophyll biosynthesis. Furthermore, the levels of trans-ferulic acid, chlorogenic acid, caffeic acid, and apigenin-7-glucoside increased in response to accumulation of As in the rice grain. In conclusion, the precise use of phosphorus may help to mitigate arsenic linked phytotoxicity and enhance the food safety aspect of rice grain.

Diversity and abundance of diazotrophic cyanobacteria in the central coastal area of the Gulf of Gabès (South-eastern Tunisia)

Gabès Gulf is limited by ultra-oligotrophic waters which are regularly fertilized with both phosphate and iron enriched atmospheric dust. Despite the lack of river run nitrogen source, an essential nutrient for the ecosystem productivity. Diazotrophic cyanobacteria are an important source of new nitrogen in oligotrophic oceans and seas. So far only the filamentous diazotrophic cyanobacteria Trichodesmium spp. has been investigated in Gabès gulf, while it is known that other diazotrophic cyanobacteria, such as the heterocysted Richelia intracellularis and unicellular cyanobacteria (UCYN), are major source of new nitrogen in oligotrophic ecosystems. In this study, we investigated the diversity and abundance of marine diazotrophic cyanobacteria within two size fractions (> 10 μm and 0.2–3​ μm) during July in the central coastal area of the Gulf of Gabès. Richelia intracellularis were present under free living and hosted in the diatoms Hemiaulus hauckii. Unicellular diazotrophic cyanobacteria were classified under tow size classes (small cells: 0.8–1.5μm and large cells: 1.6–3.2μm) with a predominance of the small cells (98 %). Richelia intracellularis reached concentrations that can be considered as a bloom phenomenon (up to 227.5 cells mL −1), while the concentration of UCYN (from 8.8 to 23.9 cells mL −1) were slightly higher than mean concentrations observed across the Mediterranean Sea. High temperature and dissolved nitrogen and orthophosphate concentrations in the central coastal area of the Gulf of Gabès seem to the main factors leading to such abundances. Contribution of each diazotrophic cyanobacteria to the N/P balance in the central coastal area of Gulf was also discussed.