Enhanced nitrogen removal in a wastewater treatment process characterized by carbon source manipulation with biological adsorption and sludge hydrolysis

Application and improvement methods of sludge alkaline fermentation liquid as a carbon source for biological nutrient removal: A review

Alkaline fermentation can reduce the amount of waste activated sludge and prepare sludge alkaline fermentation liquid (SAFL) rich in short-chain fatty acids (SCFAs), which can be used as a high-quality carbon source for the biological nutrient removal (BNR) process. This review compiles the production method of SAFL and the progress of its application as a BNR carbon source. Compared with traditional carbon sources, SAFL has the advantages of higher efficiency and economy, and different operating conditions can influence the yield and structure of SCFAs in SAFL. SAFL can significantly improve the nutrient removal efficiency of the BNR process. Taking SAFL as the internal carbon source of BNR can simultaneously solve the problem of carbon source shortage and sludge treatment difficulties in wastewater treatment plants, and further reduce the operating cost. However, the alkaline fermentation process results in many refractory organics, ammonia and phosphate in SAFL, which reduces the availability of SAFL as a carbon source. Purifying SCFAs by removing nitrogen and phosphorus, directly extracting SCFAs, or increasing the amount of SCFAs in SAFL by co-fermentation or combining with other pretreatment methods, etc., are effective measures to improve the availability of SAFL.

Seasonal and longitudinal water quality dynamics in three effluent-dependent rivers in Arizona

Effluent-fed streams, which receive inputs from wastewater treatment plants, are becoming increasingly common across the globe as urbanization intensifies. In semi-arid and arid regions, where many natural streams have dried up due to over extraction of water, many streams rely completely on treated effluent to sustain baseflow during dry seasons. These systems are often thought of as ‘second-class’ or highly disturbed stream ecosystems, but they have the potential to serve as refuges for native aquatic biota if water quality is high, especially in areas where few natural habitats remain. In this study, we investigated seasonal and longitudinal water quality dynamics at multiple sites across six reaches of three effluent-dependent rivers in Arizona (USA) with the objective (1) to quantify changes in effluent water quality due to distance traveled and season/climate and (2) to qualify whether water quality conditions in these systems are sufficient to support native aquatic species. Study reaches ranged in length from 3 to 31 km and in geographic setting from low desert to montane conifer forest. We observed the lowest water quality conditions (e.g., elevated temperature and low dissolved oxygen) during the summer in low desert reaches, and significantly greater natural remediation of water quality in longer vs. shorter reaches for several factors, including temperature, dissolved oxygen and ammonia. Nearly all sites met or exceeded water quality conditions needed to support robust assemblages of native species across multiple seasons. However, our results also indicated that temperature (max 34.2 °C), oxygen levels (min 2.7 mg/L) and ammonia concentrations (max 5.36 mg/L N) may occasionally be stressful for sensitive taxa at sites closest to effluent outfalls. Water quality conditions may be a concern during the summer. Overall, effluent-dependent streams have the capacity to serve as refuges for native biota in Arizona, and they may become the only aquatic habitat available in many urbanizing arid and semi-arid regions.

Hydrodynamic cavitation as an efficient water treatment method for various sewage:- A review

With the development of industry and the rapid growth of population, the current water treatment technologies face many challenges. Hydrodynamic cavitation as a green and efficient means of water treatment has attracted much attention. During the hydrodynamic cavitation, enormous energy could be released into the surrounding liquid which causes thermal effects (local hotspots with 4600 K), mechanical effects (pressures of 1500 bar) and chemical effects (hydroxyl radicals). These conditions can degrade bacteria and organic substance in sewage. Moreover, the combination of hydrodynamic cavitation and other water treatment methods can produce a coupling effect. In this review, we summarize the methods of hydrodynamic cavitation and the performance of water treatment for different types of sewage. The application of hydrodynamic cavitation reactors with different structures in water treatment are also evaluated and discussed. The design and optimization of high-performance hydrodynamic cavitation reactor are the most crucial issues for the application of hydrodynamic cavitation in water treatment. Finally, recommendations are provided for the future progress of hydrodynamic cavitation for water treatment.

Application of external carbon source in heterotrophic denitrification of domestic sewage: A review

The carbon source is essential as an electron donor in the heterotrophic denitrification process. When there is a lack of organic carbon sources in the system, an external carbon source is needed to improve denitrification efficiency. This review compiles the effects of liquid, solid and gaseous carbon sources on denitrification. Sodium acetate has better denitrification efficiency and is usually the first choice for external carbon sources. Fermentation by-products have been demonstrated to have the same denitrification efficiency as sodium acetate. Compared with cellulose-rich materials, biodegradable polymers have better and more stable denitrification performance in solid-phase nitrification, but their price is higher than the former. Methane as a gaseous carbon source is studied mainly by aerobic methane oxidation coupled with denitrification, which is feasible using methane as a carbon source. Liquid carbon sources are better controlled and utilized than solid carbon sources and gaseous carbon sources. In addition, high carbon to nitrogen ratio and hydraulic retention time can promote denitrification, while high dissolved oxygen (DO>2.0 mg L^-1) will inhibit the denitrification process. At the same time, high temperature is conducive to the decomposition of carbon sources by microorganisms. This review also considers the advantages and disadvantages of different carbon sources and cost analysis to provide a reference for looking for more economical and effective external carbon sources in the future.

Enhancing denitrification efficiency for nitrogen removal using waste sludge alkaline fermentation liquid as external carbon source

External carbon source was usually added to enhance denitrification efficiency for nitrogen removal in wastewater treatment. In this study, waster sludge alkaline fermentation liquid was successfully employed as an alternative carbon source for biological denitrification. The denitrification performance was studied at different C/Ns (carbon-to-nitrogen ratios) and HRTs (hydraulic retention times). A C/N of 7 and an HRT of 8 h were the optimal conditions for denitrification. The nitrate removal efficiency of 96.4% and no obvious nitrite accumulation in the effluent were achieved under the optimal conditions with a low soluble chemical oxygen demand (SCOD) level. The sludge carbon source utilization was analyzed and showed that the volatile fatty acids (VFAs) were prior utilized than proteins and carbohydrates. The excitation-emission matrix (EEM) spectroscopy with fluorescence regional integration (FRI) was adopted to analyze the compositional and variations of dissolved organic matters (DOM). Moreover, a high denitrification rate (V_DN) and potential (P_DN) with low heterotroph anoxic yield (Y_H) was exhibited at the optimal C/N and HRT condition, indicating the better denitrification ability and organic matter utilization efficiencies.

Enhancing denitrification with waste sludge carbon source: the substrate metabolism process and mechanisms

Using waste sludge internal carbon source for nitrogen removal in wastewater has drawn much attention, due to its economic advantages and sludge reduction. In this study, the performance of enhanced denitrification with waste sludge thermal hydrolysate and fermentation liquid as carbon sources at different SCOD/N (soluble chemical oxygen demand/NO₃^--N) was investigated. The optimum SCOD/N was 8 for sludge thermal hydrolysate and 7 for fermentation liquid, with NO₃^--N removal efficiency of 92.3 and 98.9%, respectively, and no NO₂^--N accumulation. To further understand the fate of sludge carbon source during denitrification, the changes of SCOD, proteins, carbohydrates, and volatile fatty acids (VFAs) were analyzed, and three-dimensional fluorescence excitation-emission matrix (EEM) spectroscopy with fluorescence regional integration (FRI) analysis was introduced. The utilization of SCOD was consistent with NO₃^--N reduction, and the utilization efficiency of different organic matter was as follows: VFAs > proteins > carbohydrates. The soluble organic-like materials (region IV) were the most readily utilized organic matter according to three-dimensional fluorescence EEM spectroscopy. Regarding denitrification mechanisms, the denitrification rate (V_DN), denitrification potential (P_DN), heterotroph anoxic yield (Y_H), and the most readily biodegradable COD (S_S) were also investigated.

Stepwise hydrolysis to improve carbon releasing efficiency from sludge

Based on thermal alkaline hydrolysis (TAH), a novel strategy of stepwise hydrolysis was developed to improve carbon releasing efficiency from waste activated sludge (WAS). By stepwise increasing hydrolysis intensity, conventional sludge hydrolysis (the control) was divided into four stages for separately recovering sludge carbon sources with different bonding strengths, namely stage 1 (60 °C, pH 6.0-8.0), stage 2 (80 °C, pH 6.0-8.0), stage 3 (80 °C, pH 10.0) and stage 4 (90 °C, pH 12.0). Results indicate stepwise hydrolysis could enhance the amount of released soluble chemical oxygen demand (SCOD) for almost 2 times, from 7200 to 14,693 mg/L, and the released carbon presented better biodegradability, with BOD/COD of 0.47 and volatile fatty acids (VFAs) yield of 0.37 g VFAs/g SCOD via anaerobic fermentation. Moreover, stepwise hydrolysis also improved the dewaterability of hydrolyzed sludge, capillary suction time (CST) reducing from 2500 to 1600 s. Economic assessment indicates stepwise hydrolysis shows less alkali demand and lower thermal energy consumption than those of the control. Furthermore, results of this study help support the concepts of improving carbon recovery in wastewater by manipulating WAS composition and the idea of classifiably recovering the nutrients in WAS.

Enhanced excess sludge hydrolysis and acidification in an activated sludge side-stream reactor process with single-stage sludge alkaline treatment: a pilot scale study

A pilot-scale side-stream reactor process with single-stage sludge alkaline treatment was employed to systematically investigate characteristics of excess sludge hydrolysis and acidification with alkaline treatment and evaluate feasibility of recovering a carbon source (C-source) from excess sludge to enhance nutrient removal at ambient temperature. The resulting C-source and volatile fatty acid specific yields reached 349.19 mg chemical oxygen demand (COD)/g volatile suspended solids (VSS) d^-1 and 121.3 mg COD/g VSS d^-1, respectively, the process had excellent C-source recovery potential. The propionic-to-acetic acid ratio of the recovered C-source was 3.0 times that in the influent, which beneficially enhanced biological phosphorus removal. Large populations and varieties of hydrolytic acid producing bacteria cooperated with alkaline treatment to accelerate sludge hydrolysis and acidification. Physicochemical characteristics indicated that recovered C-source was derived primarily from extracellular polymeric substances hydrolysis rather than from cells disruption during alkaline treatment. This study showed that excess sludge as carbon source was successfully recycled by alkaline treatment in the process.

Transformation and utilization of slowly biodegradable organic matters in biological sewage treatment of anaerobic anoxic oxic systems

This study examined the distribution of carbon sources in two anaerobic anoxic oxic (AAO) sewage treatment plants in Xi'an and investigated the transformation characteristics and utilization potential of slowly biodegradable organic matters (SBOM). Results indicated under anaerobic and aerobic conditions, SBOM could be transformed at a rate of 65% in 8h into more readily biologically utilizable substrates such as volatile fatty acids (VFAs), polysaccharides and proteins. Additionally, non-biodegradable humus-type substances which are difficult to biodegrade and readily accumulate, were also generated. These products could be further hydrolyzed to aldehyde and ketone compounds and then transformed into substances with significant oxygen-containing functional groups and utilized subsequently. The molecular weights of proteinoid substances had a wide distribution and tended to decrease over time. Long hours of microbial reaction increased the proportion of micromolecular substances. This particular increase generated significant bioavailability, which can greatly improve the efficiency of nitrogen removal.

Effects of additional fermented food wastes on nitrogen removal enhancement and sludge characteristics in a sequential batch reactor for wastewater treatment

In order to enhance nitrogen removal from domestic wastewater with a carbon/nitrogen (C/N) ratio as low as 2.2:1, external carbon source was prepared by short-term fermentation of food wastes and its effect was evaluated by experiments using sequencing batch reactors (SBRs). The addition of fermented food wastes, with carbohydrate (42.8 %) and organic acids (24.6 %) as the main organic carbon components, could enhance the total nitrogen (TN) removal by about 25 % in contrast to the 20 % brought about by the addition of sodium acetate when the C/N ratio was equally adjusted to 6.6:1. The fermented food waste addition resulted in more efficient denitrification in the first anoxic stage of the SBR operation cycle than sodium acetate. In order to characterize the metabolic potential of microorganisms by utilizing different carbon sources, Biolog-ECO tests were conducted with activated sludge samples from the SBRs. As a result, in comparison with sodium acetate, the sludge sample by fermented food waste addition showed a greater average well color development (AWCD590), better utilization level of common carbon sources, and higher microbial diversity indexes. As a multi-organic mixture, fermented food wastes seem to be superior over mono-organic chemicals as an external carbon source.

Nitrogen removal performance in planted and unplanted horizontal subsurface flow constructed wetlands treating different influent COD/N ratios

Microcosm horizontal subsurface flow constructed wetlands (HSSFCWs) were used to examine the impacts of vegetation on nitrogen dynamics treating different influent COD/N ratios (1:1, 4:1, and 8:1). An increase in the COD/N ratio led to increased reductions in NO3 and total inorganic nitrogen (TIN) in planted and unplanted wetlands, but diminished removal of NH4. The HSSFCW planted with Canna indica L. exhibited a significant reduction in NH4 compared to the unplanted system, particularly in the active root zone where NH4 removal performance increased by up to 26 % at the COD/N ratio of 8:1. There was no significant difference in NO3 removal between the planted and unplanted wetlands. TIN removal efficiency in the planted wetland increased with COD/N ratios, which was likely influenced by plant uptake. NH4 reductions were greater in planted wetland at the 20- and 40-cm depths while NO3 reductions were uniformly greater with depth in all cases, but no statistical difference was impacted by depth on TIN removal. These findings show that planting a HSSFCW can provide some benefit in reducing nitrogen loads in effluents, but only when a sufficient carbon source is present.

A new activated primary tank developed for recovering carbon source and its application

A novel activated primary tank process (APT) was developed for recovering carbon source by fermentation and elutriation of primary sludge. The effects of solids retention time (SRT), elutriation intensity (G) and return sludge ratio (RSR) on this recovery were evaluated in a pilot scale reactor. Results indicated that SRT significantly influenced carbon source recovery, and mechanical elutriation could promote soluble COD (SCOD) and VFA yields. The optimal conditions of APT were SRT=5d, G=152s(-1) and RSR=10%, SCOD and VFA production were 57.0mg/L and 21.7mg/L. Particulate organic matter in sludge was converted into SCOD and VFAs as fermentative bacteria were significantly enriched in APT. Moreover, the APT process was applied in a wastewater treatment plant to solve the problem of insufficient carbon source. The outcomes demonstrated that influent SCOD of biological tank increased by 31.1%, which improved the efficiency of removing nitrogen and phosphorus.

Enhanced nitrogen and phosphorus removal by an advanced simultaneous sludge reduction, inorganic solids separation, phosphorus recovery, and enhanced nutrient removal wastewater treatment process

An advanced wastewater treatment process (SIPER) was developed to simultaneously decrease sludge production, prevent the accumulation of inorganic solids, recover phosphorus, and enhance nutrient removal. The feasibility of simultaneous enhanced nutrient removal along with sludge reduction as well as the potential for enhanced nutrient removal via this process were further evaluated. The results showed that the denitrification potential of the supernatant of alkaline-treated sludge was higher than that of the influent. The system COD and VFA were increased by 23.0% and 68.2%, respectively, after the return of alkaline-treated sludge as an internal C-source, and the internal C-source contributed 24.1% of the total C-source. A total of 74.5% of phosphorus from wastewater was recovered as a usable chemical crystalline product. The nitrogen and phosphorus removal were improved by 19.6% and 23.6%, respectively, after incorporation of the side-stream system. Sludge minimization and excellent nutrient removal were successfully coupled in the SIPER process.

Investigation into cyclic utilization of carbon source in an advanced sludge reduction, inorganic solids separation, phosphorus recovery, and enhanced nutrient removal (SIPER) wastewater treatment process

An advanced wastewater treatment process (SIPER) was developed to simultaneously reduce sludge production, prevent the accumulation of inorganic solids, recover phosphorus, and enhance nutrient removal. The ability to recover organic substance from excess sludge to enhance nutrient removal (especially nitrogen) and its performance as a C-source were evaluated in this study. The chemical oxygen demand/total nitrogen (COD/TN) and volatile fatty acids/total phosphorus (VFA/TP) ratios for the supernatant of the alkaline-treated sludge were 3.1 times and 2.7 times those of the influent, respectively. The biodegradability of the supernatant was much better than that of the influent. The system COD was increased by 91 mg/L, and nitrogen removal was improved by 19.6% (the removal rate for TN reached 80.4%) after the return of the alkaline-treated sludge as an internal C-source. The C-source recovered from the excess sludge was successfully used to enhance nitrogen removal. The internal C-source contributed 24.1% of the total C-source, and the cyclic utilization of the system C-source was achieved by recirculation of alkaline-treated sludge in the sludge reduction, inorganic solids separation, phosphorus recovery (SIPER) process.

Evaluation of sludge reduction and carbon source recovery from excess sludge by the advanced Sludge reduction, Inorganic solids separation, Phosphorus recovery, and Enhanced nutrient Removal (SIPER) wastewater treatment process

An advanced wastewater treatment process involving Sludge reduction, Inorganic solids separation, Phosphorus recovery, and Enhanced nutrient Removal (SIPER) was developed to reduce sludge production, prevent the accumulation of inorganic solids, recover phosphorus, and enhance nutrient removal. The feasibility of recovering carbon (C)-source from excess sludge to enhance nutrient removal and the sludge reduction potential of the process was evaluated. The results showed that sludge hydrolysis and acidification yields were 20±3% and 34±2%, respectively. The COD/TN and VFA/TP ratios for the supernatant of alkaline-treated sludge were 2.8 and 2.5 times those in the influent, respectively. Nutrients were removed effectively in the system, especially TN, for which the removal efficiency reached 80±2%. The C-source recovered from the excess sludge was successfully employed as an internal C-source for enhanced nutrient removal. The observed sludge yield of the system was 0.096 g VSS g COD(-1), demonstrating the excellent sludge reduction potential of this process.

Effect of powdered activated carbon technology on short-cut nitrogen removal for coal gasification wastewater

A combined process consisting of a powdered activated carbon technology (PACT) and short-cut biological nitrogen removal reactor (SBNR) was developed to enhance the removal efficiency of the total nitrogen (TN) from the effluent of an upflow anaerobic sludge bed (UASB) reactor, which was used to treat coal gasification wastewater (CGW). The SBNR performance was improved with the increasing of COD and TP removal efficiency via PACT. The average removal efficiencies of COD and TP in PACT were respectively 85.80% and 90.30%. Meanwhile, the NH3-N to NO2-N conversion rate was achieved 86.89% in SBNR and the total nitrogen (TN) removal efficiency was 75.54%. In contrast, the AOB in SBNR was significantly inhibited without PACT or with poor performance of PACT in advance, which rendered the removal of TN. Furthermore, PAC was demonstrated to remove some refractory compounds, which therefore improved the biodegradability of the coal gasification wastewater.

The effects of wavelength and wavelength mixing ratios on microalgae growth and nitrogen, phosphorus removal using Scenedesmus sp. for wastewater treatment

In wastewater treatment using microalgae, the effects of wavelength and wavelength mixing ratio on microalgae growth and removal of nitrogen and phosphorus were evaluated using LEDs (white light, 670nm, 450nm, and 525nm). Microalgae production rates were enhanced by a maximum of 45% with 400-700nm white light compared to that of a single wavelength. The phosphorus removal rate was as high as 90% with blue light. When red light and blue light were mixed and supplied, the microalgae production rate was about 50% higher than the rate of the culture with white light. Nitrogen and phosphorus removal rates were as high as approximately 15mg/L/day at a wavelength mixing ratio of 7 (red light):3 (blue light) and 2.1mg/L/day at a wavelength mixing ratio of 5 (red light):5 (blue light).

Waste activated sludge hydrolysis during ultrasonication: two-step disintegration

In order to clearly describe the hydrolysis of waste activated sludge (WAS) during ultrasonication by a 2-step disintegration process, concentrations of ribonucleic acid (RNA) and bound extracellular polymeric substance (EPS) were measured. Apparently, different decreasing patterns of RNA and EPS concentrations during WAS hydrolysis made it possible to distinguish the floc disintegration (FD) and cell lysis (CL). Initially, FD and CL appear to take simultaneously, but the dominant hydrolytic process is shifted from FD to CL after 10 min of ultrasonication. Additional kinetic analysis of WAS hydrolysis was also conducted. A five-fold greater hydrolysis rate constant of FD relative to that of CL was observed, reflecting the different strengths of floc and cells. Therefore, different rates of increased solubilization during WAS hydrolysis appear to account for the initial disintegration of the rather loose part (sludge floc) and the subsequent disintegration of the rigid part (microbial cells).