Tracking the inorganic suspended solids through biological treatment units of wastewater treatment plants

From an experimental and theoretical investigation of the continuity of influent inorganic suspended solids (ISS) along the links connecting the primary settling tank (PST), fully aerobic or N removal activated sludge (AS) and anaerobic and aerobic digestion (AerD) unit operations, it was found that (i) the influent wastewater (fixed) ISS concentration is conserved through primary sludge anaerobic digestion, and AS and AerD unit operations. However, the measured ISS flux at different stages through a series of WWTP unit operations is not equal to the influent ISS flux because the ordinary heterotrophic organisms (OHO) biomass contributes to the ISS flux by differing amounts depending on the OHO (active) fraction of the VSS solids at that stage.     

Incorporation of inorganic material in anoxic/aerobic-activated sludge system mixed liquor

In the bioreactor of the nitrification denitrification (ND)-activated sludge system, the mixed liquor is made up of organic and inorganic materials. In the current design procedures and simulation models, the influent wastewater characteristics and biological processes that influence the bioreactor mixed liquor organic solids (as volatile suspended solids, VSS, or COD) are explicitly included. However, the mixed liquor total suspended solids (TSS, i.e. organic+inorganic solids) are calculated simply from empirical ratios of VSS/TSS. The TSS concentration is fundamental in the design of secondary settling tanks and waste activated sludge disposal. Clearly, the empirical approach to obtaining an estimate for TSS is not satisfactory within the framework of a fundamentally based model. Accordingly, the incorporation of the inorganic material present in the influent wastewater into ND-activated sludge system mixed liquor was investigated. From an experimental investigation into the distribution of inorganics in the influent, mixed liquor and effluent of a laboratory-scale ND-activated sludge system, it was concluded inter alia that (i) of the total inorganic solids in the influent, only a small fraction (2.8–7.5%) is incorporated into the mixed liquor, (ii) most of the inorganics in the influent (mean 88%) and effluent (mean 98.5%) are in the dissolved form, the balance being particulate, and (iii) the influent and effluent inorganic dissolved solids concentrations are closely equal (mean effluent to influent ratio 100%). Further, a number of models were developed to quantify the mixed liquor inorganic, and, hence, total solids. From an evaluation of these models against the experimental data, it would appear that the best approach to model the incorporation of inorganics into the activated sludge mixed liquor is to follow the concepts and principles used to develop the existing models for organic materials. With this approach, reasonably close correlation between predicted and measured data for mixed liquor and effluent inorganic concentrations were obtained.     

Aerobic digestion of thickened activated sludge: Reaction rate constant determination and process performance

The aims of this work were to select which parameter—total suspended solids (TSS), volatile suspended solids (VSS) or degradable volatile suspended solids (DVSS)—best expressed the kinetics of aerobic digestion of waste secondary activated sludge: to define the relationship between the reaction rate constant and the initial concentration of sludges; to evaluate the effect of aerobic digestion on the filterability of the treated sludge as measured by the capillary suction time (C.S.T.).Batch experiments of aerobic digestion were performed in our laboratory on samples of sludges at a constant temperature of 20 C. The initial concentration of sludges ranged from 2600 to 22,000 mg l⁻¹.TSS was found to be the parameter which most closely fits the kinetic model of aerobic digestion. The reaction rate constant was a linear, inverse function of the initial sludge concentration with TSS and with VSS as a parameter.Sludge filterability is affected by the process of aerobic digestion; a prolonged aeration time results in poorer dewatering; and the more concentrated the sample, the poorer the dewatering.     

Suspended solids in Missouri reservoirs in relation to catchment features and internal processes

Mean total suspended solids (TSS), in 135 Missouri reservoirs range from 1.2 to 47 mg/l. The volatile (VSS) and non-volatile (NVSS) fractions range from 0.6 to 9.6 mg/l and 0.5 to 37 mg/l, respectively. %NVSS is the larger fraction and declines through summer as %VSS increases. Suspended solids (particularly VSS) correlate with metrics of lake trophic state and are positively related with the proportion of cropland (%C, r = 0.69-0.74) in their catchments, negatively related with forest cover (r = -0.54 to -0.56), and weakly related with grassland (r < 0.31). Regressions including %C with dam height (representing morphometry) and flushing rate (representing hydrology), explain approximately 70% of cross-system variation in TSS and 67% in VSS. Dam height and %C explain 57% of variation in NVSS. Residual analysis shows statewide models under-predict suspended solids in urban reservoirs. Effects of catchment features on summer TSS largely reflect internal plankton growth mediated by influent nutrients (affecting VSS) over direct sediment input (affecting NVSS).     

Sludge viability in a biological reactor

The volatile suspended solids (VSS) concentration cannot be used as a measure for the active biomass in a reactor which operates under a wide range of operating conditions since the viable organism content of the VSS is not constant. Using substrate saturation conditions the kinetic parameters maximum substrate removal rate ( ) and oxygen uptake rate (J)—both per mass of VSS—were determined in an experimental pulse fed batch biological reactor. It was found that and J both doubled during the experimental period (6 h). It was concluded that the increases in and J values were due to the increase in the sludge viability which are here defined as the percentage of VSS which is active biomass. Using the variations in and J values during each experiment, it was possible to calculate sludge viability. During a 6 h experimental period at substrate saturation level the sludge viability increased on average from 8.9 to 23.3%.In a loop type sewage conduits system operated as a plug flow reactor and enriched with biomass and air, it is possible to achieve high specific substrate removal rates when step feeding creates saturation conditions. This is further attenuated by a marked increase in the sludge viability.     

Performance evaluation of an oily industrial wastewater treatment system using the application of activated sludge model No. 3

The purpose of the present study was to adapt the activated sludge model No. 3 (ASM3) to the characteristics of oily industrial wastewater, determining the utmost significant and appropriate kinetic as well as stoichiometric parameters. An oily industrial wastewater treatment system was simulated to assess ASM3 validation and perform sensitivity analysis using the STOAT program. The obtained results revealed that the ASM3 model, which was calibrated after adding the Arrhenius equation into consideration, provided strong correlations with the analytical results of chemical oxygen demand (COD), total suspended solids (TSS), mixed liquor volatile suspended solids (MLVSS) and total suspended solids in the return activated sludge flow (TSS in RAS) concentrations. The values of modelled effluent COD and TSS are very close to those corresponding real values of the treated wastewater by a difference of between 0.5% and 1.5%. Thus, this model becomes successful in representing oily industrial wastewater treatment as a new trend added to the traditional modelling of sewage treatment.     

Interactions between calcium precipitation and the polyphosphate-accumulating bacteria metabolism

A sequencing batch reactor that is operated for biological phosphorus removal has been operated under different influent calcium concentrations to study the precipitation process and the possible effects of phosphorus precipitation in the biological phosphorus removal process. Four experiments were carried out under different influent calcium concentrations ranging from 10 to 90 g Ca m(-3). The experimental results and the equilibrium study, which are based on the saturation index calculation, confirm that the process controlling the calcium behaviour is the calcium phosphate precipitation. This precipitation takes place at two stages: initially, precipitation of the amorphous calcium phosphate, and later crystallization of hydroxyapatite. Also the accumulation of phosphorus precipitated was observed when the influent calcium concentration was increased. In all the experiments, the influent wastewater ratio P/COD was kept constant. It has been observed that, at high calcium concentration, the ratio between phosphate release and acetate uptake (P(rel)/Ac(uptake)) decreases. Changes in the polyphosphate-accumulating organism (PAO) population and in the glycogen-accumulating organism (GAO) population during the experimental period were ruled out by means of fluorescence in situ hybridization. These results could suggest that PAO are able to change their metabolic pathways based on external conditions, such as influent calcium concentration. The accumulation of phosphorus precipitated as calcium phosphate at high influent calcium concentration throughout the experimental period confirmed that phosphate precipitation is a process that can affect the PAO metabolism.     

Solids characterisation in an anaerobic migrating bed reactor (AMBR) sewage treatment system

The aim of this work was to characterise the solids in an anaerobic sewage treatment process. Hindered settling velocity, particle size distributions (PSD), influent and effluent COD(P)/SS and discrete settling velocity distributions were all measured. The anaerobic migrating bed reactor (AMBR) solids were mainly flocculent and had a settling rate equivalent to a good settling activated sludge ( approximately SSVI=60 mL/g). The PSD of the anaerobic solids were very different to PSD for activated sludge flocs, with the anaerobic solids having a modal size an order of magnitude smaller than activated sludge, but a range of particle sizes being two orders of magnitude larger. There was a far greater range in size and structure in the anaerobic solids. The anaerobic process solids were primarily feed solids undergoing VSS destruction (hydrolysis). The biological mass was small. The solids seemed to retain their size as the volatiles were degraded and the density decreased ('skeletons' of the influent particulates). The small fraction of slowly settling solids, which have been identified to have a similar modal size but lower density than the mixed solids in the reactor, pose a solids retention time (SRT) control problem when relying on settling alone for solids retention.     

基于工艺模拟的污水处理厂数字化实例研究

在对污水处理厂历史监测数据收集、整理和分析的基础上,利用GPS-X软件,建立并校正了污水处理厂工艺模型,同时探索了校正方法。研究结果表明,自养菌最大比生长速率作为污水特征参数,需通过拟合出水的NH3-N浓度变化进行校准。污泥浓度的拟合是一个非常重要的步骤,影响污泥浓度拟合的参数包括进水特征参数(VSS/TSS值、总COD中颗粒惰性组分的占比)、剩余污泥排放量、初沉污泥排放量。     

Modelling of the activated sludge process for microprocessor-based state estimation and control

A simple dynamic model of the activated sludge process including the volatile suspended solids (VSS) concentration in the aeration basin, the VSS or suspended solids (SS) concentration in the recycle flow and the SS concentration in the effluent was obtained by simplifying a comprehensive model using empirically verified assumptions. The model can be used for on-line estimation of the influent BOD-load and the effluent BOD, in combination with a recursive algorithm for oxygen uptake rate (OUR) and k_La estimation requiring only dissolved oxygen and air flow rate measurements. The estimation procedure has been implemented and tested at a real plant using a microprocessor. Control of the activated sludge process is discussed and concluded to be a hierarchical two-level problem. The upper level control actions are aimed at bringing the process to an optimal state of operation. For this purpose verbally formulated control laws are used. On the lower level the control task is to maintain the process in the optimal state.     

Full-scale trials of recycled glass as tertiary filter medium for wastewater treatment

Pilot-scale trials at a domestic wastewater treatment works compared the performance of three grades of recycled glass (coarse, medium and fine) when used as tertiary filter media for total suspended solids removal (TSS). Fine glass produced the best effluent quality but blinded rapidly and coarse glass could process three times the flow but with a reduction in final effluent quality. The medium glass offered a compromise with similar flow characteristics to the coarse glass, yet still achieve good solids removal, albeit less than the fine glass. Full-scale studies compared the performance of medium glass with the sand medium that is typically used in this application. There was little difference between them in terms of TSS removal, and they both removed around 75% of TSS from the influent, provided that the solids concentration did not exceed 70mg/l. However, the glass media had superior flow characteristics and was able to treat an additional 8-10% of the influent following the backwash cycle. Over the study period, the influent to the filters had an average TSS concentration of 38mg/l and produced an effluent with an average of 15mg TSS/l. In order to design for an average TSS concentration of 20mg/l, the maximum solids loading on the medium should not exceed 0.25kg solids/m(3)/h. Selecting recycled glass as a tertiary filter medium will give a 10% reduction in the amount of media required, compared to sand. It also carries with it the benefits of using a recycled material, and although these are more difficult to quantify they include: reduced CO(2) emissions and use of a more sustainable product that promotes favourable publicity and positive environmental reporting.     

Treatment of high strength acidic wastewater with a completely mixed anaerobic filter

A completely mixed anaerobic filter, in which the influent organic matter concentration is diluted with recirculated effluent, was found to effectively remove organic matter concentrations in high strength acidic wastewater, at a range of organic loadings and shockloads. The methane in the generated gas accounted for 93% of the COD removal in the unit, while a solids balance indicated that only 0.012 g VSS was produced per g COD removed. Due to the low solids production and the initial seeding of the unit with digested sludge no nutrient additions were required during the 518 day period even though the COD:P and COD:N ratios were as high as 4360:1 and 39:1, respectively. Although a possible heavy metal toxicity was observed in the unit, this was eliminated after sulfide addition.     

Color removal from cotton textile industry wastewater in an activated sludge system with various additives

The low biodegradability of many dyes and textile chemicals indicates that biological treatment is not always successful in the treatment of cotton textile wastewater, in terms of color removal. In this study, a specific organic flocculant (Marwichem DEC), powdered activated carbon (PAC), bentonite, activated clay and commercial synthetic inorganic clay (Macrosorb) were directly added into the activated sludge laboratory pilot plant model. Before dosage, the optimum sludge retention time and hydraulic retention time were determined as 30 days and 1.6 days, respectively. The Monod kinetic constants were determined as Y = 0.76 kg MLSS/kg COD, Kd = 0.026 l/day, K(S) = 113.3 mg/L, k = 0.42 l/day and mu(max) = 0.32 kg MLSS/kg COD day. Under these conditions the average COD removal was 94% and color removal was 36%. The addition of these materials did not change COD removal significantly. The most effective materials were found to be DEC and PAC for color removal. While the color removal efficiency for 120 mg/L DEC addition was 78%, it was 65% for 100 mg/L, 77% for 200 mg/L and 86% for 400 mg/L PAC addition. The advantage of DEC compared to PAC was the lower sludge production. Statistical analyses using multiple linear regression indicate that there is no relationship between the effluent color with the influent color and total suspended solids (TSS) for DEC and PAC addition. On the other hand, when only bentonite, activated clay and Macrosorb were added, the effluent color was primarily dependent on the influent color and the TSS concentration had little effect. When the data is examined by using Kruskal-Wallis H and Mann-Whitney U tests and it was found that there was a significant difference between the color data groups.     

Aerobic stabilization of primary and mixed primary-chemical (alum) sludge

This study was conducted to investigate the feasibility of using aerobic digestion as a method for the stabilization of mixed primary-chemical (alum) sludge from a physical-chemical treatment plant. Aerobic digestion was carried out in “continuous” flow (batch fed once a day) laboratory reactors with detention times ranging from 5 to 35 days held at 7, 12, 18 and 25°C.Temperature was found to have a slightly greater influence on the reduction of volatile suspended solids in primary sludge than in mixed primary-chemical sludge. Nitrification took place in the reactors treating both primary and mixed primary-chemical sludge. The high content of aluminum in the mixed primary-chemical sludge did not inhibit the nitrifiers. The oxygen-uptake rate varied between approximately 5 mg O₂ g⁻¹ VSS h⁻¹ and 1 mg O₂ g⁻¹ VSS h⁻¹ depending on the detention time and the reactor temperature. Adenosine triphosphate content per unit volatile suspended solids indicated a low content of active biomass during aerobic digestion.     

The effect of primary sedimentation on full-scale WWTP nutrient removal performance

Traditionally, the performance of full-scale wastewater treatment plants (WWTPs) is measured based on influent and/or effluent and waste sludge flows and concentrations. Full-scale WWTP data typically have a high variance which often contains (large) measurement errors. A good process engineering evaluation of the WWTP performance is therefore difficult. This also makes it usually difficult to evaluate effect of process changes in a plant or compare plants to each other. In this paper we used a case study of a full-scale nutrient removing WWTP. The plant normally uses presettled wastewater, as a means to increase the nutrient removal the plant was operated for a period by-passing raw wastewater (27% of the influent flow). The effect of raw wastewater addition has been evaluated by different approaches: (i) influent characteristics, (ii) design retrofit, (iii) effluent quality, (iv) removal efficiencies, (v) activated sludge characteristics, (vi) microbial activity tests and FISH analysis and, (vii) performance assessment based on mass balance evaluation. This paper demonstrates that mass balance evaluation approach helps the WWTP engineers to distinguish and quantify between different strategies, where others could not. In the studied case, by-passing raw wastewater (27% of the influent flow) directly to the biological reactor did not improve the effluent quality and the nutrient removal efficiency of the WWTP. The increase of the influent C/N and C/P ratios was associated to particulate compounds with low COD/VSS ratio and a high non-biodegradable COD fraction.     

高效初沉发酵池处理城市污水的中试研究

应用生物絮凝沉淀和水解发酵耦合工艺,将传统的初沉池改造为集进水悬浮固体的沉淀分离和沉淀污泥的产酸发酵为一体的高效初沉发酵池,以优化碳源结构,提高后续工艺的污泥活性和脱氮除磷能力。在水力停留时间为0.75 h、悬浮污泥絮体层界面高度不低于高效初沉发酵池有效池深的70%、SRT为4 d的条件下,考察了高效初沉发酵池对进水水质的改善效果。结果表明:高效初沉发酵池对SS的去除率为78%,是普通初沉池的近2倍;出水VSS/SS均值为71.9%,较普通初沉池提高了17.3%;出水C/N和C/P值较进水值分别提高了33%和14%,且明显高于污水厂普通初沉池出水水质。碳源结构的改善提高了后续生物处理工艺的脱氮除磷效果,对TP的去除率稳定在90%～98%。     

Anaerobic treatment of phenol in wastewater under thermophilic condition

Over 99% of phenol was effectively degraded in an upflow anaerobic sludge blanket (UASB) reactor at 55 degrees C with 40 h of hydraulic retention time (HRT) for a wastewater containing 630 mg/L of phenol, corresponding to 1500 mg/L of chemical oxygen demand (COD) and a loading rate of 0.9 g-COD/L/d. The maximum specific methanogenic activity (SMA) of the phenol-degrading sludge was 0.09 g-CH4-COD/g-volatile suspended solids (VSS)/d. Based on 16S rDNA analysis, a total of 21 operational taxonomy units (OTUs) were found in the sludge, of which eight (42.6% of the total population) were related to the sequences in the GenBank with similarity of over 97%, and 13 (79.6%) were affiliated with the known thermophilic species. Additional SMA data and phylogenetic analysis suggest that the degradation pathway of phenol for thermophilic sludge was likely via caproate, instead of benzoate as for the mesophilic sludge.     

Source identification of heavy metals in sewage sludge and the effect of influent characteristics: a case study from China

To advance the reclamation of sewage sludge and evaluate the potential risk during sludge application, wastewater and sludge were sampled from seven secondary wastewater treatment plants seasonally in 2016 and 2017. The influent characteristics and the accumulation of eight toxic heavy metals in sludge were analyzed. According to the results, copper, chromium, nickle and zinc were the main heavy metals constraining reclamation of sewage sludge in Shanghai and they were mainly from domestic wastewater. Influent concentration, treatment process and coexisting elements had significant effects on accumulation of heavy metals in sludge. Lead concentration in sludge from AAC plants was generally higher than that from AAO plants, but for other metals the differences were insignificant or depended on the initial concentrations. Nutrients, suspended solids and coexisting heavy metals had significant effects on heavy metal accumulation in sludge when the initial concentration was controlled.     

Ammonium adsorption in aerobic granular sludge, activated sludge and anammox granules

The ammonium adsorption properties of aerobic granular sludge, activated sludge and anammox granules have been investigated. During operation of a pilot-scale aerobic granular sludge reactor, a positive relation between the influent ammonium concentration and the ammonium adsorbed was observed. Aerobic granular sludge exhibited much higher adsorption capacity compared to activated sludge and anammox granules. At an equilibrium ammonium concentration of 30 mg N/L, adsorption obtained with activated sludge and anammox granules was around 0.2 mg NH₄-N/g VSS, while aerobic granular sludge from lab- and pilot-scale exhibited an adsorption of 1.7 and 0.9 mg NH₄-N/g VSS, respectively. No difference in the ammonium adsorption was observed in lab-scale reactors operated at different temperatures (20 and 30 °C). In a lab-scale reactor fed with saline wastewater, we observed that the amount of ammonium adsorbed considerably decreased when the salt concentration increased. The results indicate that adsorption or better ion exchange of ammonium should be incorporated into models for nitrification/denitrification, certainly when aerobic granular sludge is used.     

Enhanced settleability and dewaterability of fungal treated domestic wastewater sludge by liquid state bioconversion process

A study was conducted to evaluate the settleability and dewaterability of fungal treated and untreated sludge using liquid state bioconversion process. The fungal mixed culture of Aspergillus niger and Penicillium corylophilum was used for fungal pretreatment of wastewater sludge. The fungal strains immobilized/entrapped on sludge particles with the formation of pellets and enhanced the separation process. The results presented in this study showed that the sludge particles (pellets) size of 2-5mm of diameter were formed with the microbial treatment of sludge after 2 days of fermentation that contained maximum 33.7% of total particles with 3-3.5mm of diameter. The settling rate (measured as total suspended solids (TSS) concentration, 130 mg/l) was faster in treated sludge than untreated sludge (TSS concentration, 440 mg/l) after 1 min of settling time. In 1 min of settling operation, 86.45% of TSS was settled in treated sludge while 4.35% of TSS settled in raw sludge. Lower turbidity was observed in treated sludge as compared to untreated sludge. The results to specific resistance to filtration (SRF) revealed that the fungal inoculum had significant potentiality to reduce SRF by 99.8% and 98.7% for 1% w/w and 4% w/w of TSS sludge, respectively. The optimum fermentation period recorded was 3 days for 1% w/w sludge and 6 days for 4% w/w sludge, respectively, for dewaterability test.