Sludge Loading Research Articles

Impact of food-to-microorganisms ratio on the stability of aerobic granular sludge treating high-strength organic wastewater

This work investigated the long-term stability of aerobic granular sludge treating high-strength organic wastewater in a semi-pilot scale sequential batch reactor (SBR). The reactor was operated for 316 days under different operational conditions. It was found that the F/M ratio is an important parameter affecting granules formation and stability. Three selection mechanisms were investigated: (1) cultivation and maturation at moderately high influent COD concentration (2500 mg/L) followed by increase in influent COD concentration to 7500 mg/L; (2) stressed cultivation and operation at high influent COD concentration of 4500 mg/L; and (3) alternate feed loading strategy (variable influent COD concentration across the daily schedule of cycles at 50%, 75%, and 100% of the peak concentration of 5000 mg/L). It was found that adopting high OLR at the reactor start-up accelerated the formation of granules. However, the overgrowth of biomass under high organics concentration negatively affected the stability of granules and led to disintegration due to the presence of methanogens in the granule core. Cultivation at high organics concentration resulted in a rapid loss of microbial diversity and reactor failure. Under alternate feed loading, adequate selection of microbial community was maintained and resulted in stable reactor performance. Moreover, a strong correlation between F/M ratio and the granules settling ability was observed. When F/M ratio exceeded 1.5 gCOD/gSS.d, granules showed poor settleability and under very high sludge loading rates (above 2.5), sludge bulking occurred and led to washout of sludge due to the strong selection pressure of short settling time. Operating the reactor at F/M ratio of 0.5–1.4 gCOD/gSS.d appears to favor stable long-term granule stability.

Conversion of Food Processing Waste to Bioenergy: Bangladesh Perspective

Microbial fuel cell (MFC) is an attractive renewable and sustainable technology to meet up the drastic energy crisis of the world through waste water treatment. This Bioelectrochemical system (BES) converts biomass spontaneously into electricity by the metabolic activity of microorganisms. Food processing industry generally discharges large volume of wastewater, which creates adverse financial and ecological impacts to the industry and environment. In this present contribution, electricity production from food processing industry wastewater that serves as substrates in MFCs was investigated. Dual chambered mediator-less MFC was designed and fabricated using locally available materials. Performance of the MFC was evaluated by measuring potential parameters, such as current generation, current density, change in pH, and change in chemical oxygen demand at different operating conditions. Polarization experiments were conducted to find the maximum power density. Current generation increased with increasing sludge loading, and maximum results were recorded as 90 µA with 9 g of sludge and optimum pH value 8 in the anode chamber. This study documented a maximum power density of 7.42 mW/m 2 with the corresponding current density of 25 mA/m 2 . Citation: Amin, M. S. A., Talukder, M. J., Raju, R. R., and Khan, M. M. R. (2019). Conversion of Food Processing Waste to Bioenergy: Bangladesh Perspective. Trends in Renewable Energy, 5(1), 1-11. DOI: 10.17737/tre.2019.5.1.0080

A Feasible Data-Driven Mining System to Optimize Wastewater Treatment Process Design and Operation

Achieving low costs and high efficiency in wastewater treatment plants (WWTPs) is a common challenge in developing countries, although many optimizing tools on process design and operation have been well established. A data-driven optimal strategy without the prerequisite of expensive instruments and skilled engineers is thus attractive in practice. In this study, a data mining system was implemented to optimize the process design and operation in WWTPs in China, following an integral procedure including data collection and cleaning, data warehouse, data mining, and web user interface. A data warehouse was demonstrated and analyzed using one-year process data in 30 WWTPs in China. Six sludge removal loading rates on water quality indices, such as chemical oxygen demand (COD), total nitrogen (TN), and total phosphorous (TP), were calculated as derived parameters and organized into fact sheets. A searching algorithm was programmed to find out the five records most similar to the target scenario. A web interface was developed for users to input scenarios, view outputs, and update the database. Two case WWTPs were investigated to verify the data mining system. The results indicated that effluent quality of Case-1 WWTP was improved to meet the discharging criteria through optimal operations, and the process design of Case-2 WWTP could be refined in a feedback loop. A discussion on the gaps, potential, and challenges of data mining in practice was provided. The data mining system in this study is a good candidate for engineers to understand and control their processes in WWTPs.

Control strategy for filamentous sludge bulking: Bench-scale test and full-scale application

Sludge bulking caused by the overgrowth of filamentous bacteria, especially Microthrix parvicella, has been observed in WWTPs worldwide during low-temperature periods. In this study, the impacts of sludge load on the in situ growth of M. parvicella and sludge settleability were first evaluated at 15 °C over a period of 500 d using a bench-scale anaerobic-anoxic-aerobic reactor fed with raw sewage from a full-scale WWTP. When the reactor was operated at a sludge load of 0.07 ± 0.015 kg Chemical Oxygen Demand (COD) (kg MLSS·d)−1 for 120 d, the sludge volume index (SVI) increased gradually from 85 mL g−1 to 157 mL g−1, and the abundance of M. parvicella quantified by qPCR and FISH methods also increased from 0.42% to 4.63% and 1.56%–13.59%, respectively. When the sludge load was further reduced to 0.04 ± 0.004 kg COD (kg MLSS·d)−1, the SVI value varied in a narrow range of 135–164 mL g−1 over a duration of 280 d, while the M. parvicella abundance increased to the maximum values of 10.13% (qPCR) and 18.53% (FISH), respectively. When the sludge load was increased to 0.12 ± 0.016 kg COD (kg MLSS·d)−1, filamentous abundance and SVI were reduced to 1.06% (qPCR) and 105 mL g−1 within 100 d, suggesting that it might be possible to control the growth of M. parvicella by keeping the sludge load above 0.1 kg COD (kg MLSS·d)−1. The feasibility of the strategy was further validated in the same WWTP. It was found that the SVI and filamentous abundance in winter were successfully controlled for two successive years at below 120 mL g−1 and 7% (FISH), respectively, when the sludge load was maintained at 0.14 ± 0.04 kg COD (kg MLSS·d)−1 by adjusting sludge discharge, proving that this sludge-load-based strategy could be an efficient approach to control filamentous bulking.

Factors affecting Accumulibacter population structure in full- and laboratory-scale biological reactors with nutrients removal.

The structure of Accumulibacter lineage was examined over a three-year period in six full-scale wastewater treatment plants and compared to the population in a laboratory-scale reactor. The Accumulibacter lineage reached 69% of all bacteria in the laboratory-scale reactor and contained clades IA and IIA,C,D only. In full-scale plants, Accumulibacter constituted up to 12%, correlated with sludge loading with BOD, COD, N and P. Clade IA was more abundant after periods with low temperatures, whereas clades IIA,C,D presented opposite variations. The fraction, unrevealed by clade-specific probes, constituted 31-62% of the Accumulibacter lineage in all but one full-scale plant - the population in the plant with significant industrial contribution in the influent resembled the low diversity in the laboratory-scale reactor. Selection of specific clades in the laboratory-scale reactor was associated with its different performance, despite stable operational conditions being maintained through the study. It implies that high relative abundance of Accumulibacter in bacterial community is not enough for efficient P removal and the effectiveness may also be associated with the presence of specific clades. A considerable fraction of Accumulibacter in full-scale plants, which is not targeted by clade-specific probes, should be further investigated to better characterize clades that may affect effectiveness of phosphorus removal.

Analysis on the operating characteristics of improved UASB to treat the thermal dehydration wastewater of sludge

In order to investigate COD removal efficiency and production capacity of energy, the anaerobic sludge bed reactor with high diameter ratio of 10 was used to treat the thermal dehydration wastewater (TDW) of sludge. The experiment was divided into 7 stage, the results showed that on the condition of the acclimated sludge, the reactor would be stable after 25 days; then the maximum removal rate of COD was up to 68%, the maximum amount of Nissan CH4 was 575.53 ml/L, and methane production ratio was 104.05ml/(g CODd). The concentration of ammonia nitrogen (NH4+-N) was the main factor affected the stable operation of the reactor. When the concentration of NH4+-N reached 1.5g/L, the inhibition phenomenon to methanogenic bacteria appeared. And when it was up to 2.4g/L, the methanogenic bacteria were seriously inhibited. The optimal sludge loading of the experiment was 0.10∼0.24 kg COD/(kg Sludged), and the optimal volume load was 5∼13 kg COD/(m3·d).

Effect of Sewage Sludge Amended Soil on Maize Crop I. Influence on yield and mineral nutrition

The aim of the present study was to evaluate the efficiency of sewage sludge application on maize (Zea Mays L.) growth, yield and macroelements accumulation (N, P, K, Ca, Mg) when different doses of sewage were applied accompanied by mineral fertilization. The results indicated that sewage sludge fertilization produces significant increase of maize yield that are evident starting with 200 kg N/ha rate, and the highest increases were recorded in the rate of 400 kg N/ ha. The nitrogen content in the maize leaves increased significantly in the variants fertilized with sludge at a rate over 300 kg N/ha, meanwhile the potassium content of the maize leaves was significantly reduced as a result of sludge fertilization at a rate equivalent to 400 kg N/ha. Nitrogen and phosphorus contents in the maize kernels increased with sewage sludge loading, meanwhile in the case of potassium the data showed that there were no statistically significant changes in the potassium content of the maize kernels under the influence of sewage sludge fertilization. The application of sewage sludge caused a significant increase of the calcium and magnesium contents in the maize leaves at equivalent rates higher than 200 kg/N ha.

Strategies for improving nitrogen removal under high sludge loading rate in an anammox membrane bioreactor operated at 25 °C

An anaerobic ammonium oxidation (anammox) membrane bioreactor operated at 25 °C was used to investigate nitrogen removal under different operation conditions, namely, different sludge retention time (SRT) and nitrogen loading rate (NLR). The inhibition processes caused by high substance concentrations and over-loading were able to be circumvented by various adjustment methods. Furthermore, specific anammox activity (SAA) tests were performed to evaluate the effects of ammonium and nitrite on the anammox sludge. Over an SRT of 500 d, the content of volatile suspended solids (VSS) gradually increased from 125 mg/L to 5590 mg/L, and the maximum nitrogen removal rate (NRR) reached 1.18 kg N/m3/d. When the SRT was decreased to 50 d, the sludge concentration declined gradually, which necessitated an increase in the sludge loading rate (SLR), and the maximum sludge nitrogen removal rate (SNRR) of 0.67 g total nitrogen (TN)/g VSS/d was achieved at this time.

Implementing an Odor Control Program for a Centralized Sludge Processing and Loading Facility

Implementing an Odor Control Program for a Centralized Sludge Processing and Loading Facility

WATER TREATMENT SLUDGE AS POTENTIAL SOIL AMENDMENT FOR NATIVE PLANTS OF THE BRAZILIAN CERRADO

This work evaluates the effect of 5 mixtures of water treatment sludge, soil from the Cerrado region (Brazil) and a commercial substrate on the growth of 4 species of native plants (Copaifera langsdorffii, Astronium fraxinifolium, Peltophorum dubium and Tabebuia roseo-alba) from the Brazilian Cerrado. A randomized design was setup with four repetitions and WTS loading rates of 0, 204, 417, 638 and 869 g/kg. Plant sampling for analysis was performed at 30, 60, 90, 120 and 150 days after planting, totalling 400 experiments. The results on morphological parameters and foliar analysis showed good results for the sludge loading rates of 204 and 417 g/kg (18,75 and 37,5% of sludge, respectively), for the Copaifera langsdorffii, Astronium fraxinifolium and Tabebuia roseo-alba growth, which presented the highest values for plant diameter, height and total dry matter weight at the 90th and 120th day of experiments. These loading rates seem to provide suitable buffer conditions and nutrients for plant growth. For sludge loading rates of 638 and 869 g/kg the development of all species was reduced, suggesting that plant growth was probably affected by both the higher concentration of Al and the poor mixture structure due to excess of sludge.

Insights into the applicability of microbial fuel cells in wastewater treatment plants for a sustainable generation of electricity

ABSTRACTMicrobial fuel cells (MFCs) are often discussed as a part of a sustainable generation of electricity for the coming ‘energy revolution’. In particular, the application of MFCs in wastewater treatment plants (WWTPs) are often regarded as an attractive alternative to reduce costs while generating electricity. Field surveys are necessary to show the applicability of MFCs in WWTPs considering daily fluctuations and environmental effects such as rain events affecting the MFC performance remarkably. In this study, a MFC system was tested in four municipal WWTPs using different modes of operation. A correlation between current densities and sludge loading (SL) was identified. At low SLs, the activated sludge needs a large amount of the energy derived from the substrate for the maintenance metabolism resulting in quite low current densities of the MFC. At high SLs much more of the energy can be transferred from the activated sludge to the electrode, resulting in higher currents. Furthermore, the effect of environmental conditions on the current densities was evaluated. WWTPs have daily fluctuations depending on the wastewater composition, weather phenomena and population equivalents. Our data show that these daily fluctuations can only be observed in the MFC performance at WWTPs below 50,000 population equivalents.

Biogas Production Experimental Research by Using Sewage Sludge Loading with Biochar Additive

Biogas – ecological fuel, which is assigned to alternative energy sources. It should be noted, that biogas – renewable energy source, which does not require any specific climatic conditions or geographical position of a country. This power source is available and can be successfully produced and used in all countries of the world. The main components of biogas – methane CH4 and carbon monoxide CO2. This gas is formed under anaerobic conditions, when microorganisms decompose biodegradable biomass. In biological sciences biomass means a living matter content, expressed in grams per unit area. Meanwhile, in the energy sector, the definition of biomass is limited and biomass is characterized as fuel source, produced from plant materials and organic waste (food waste, wood, sludge, manure, vegetables, etc.). Currently, to produce biogas from biomass, bioreactors are used worldwide. However, in order to increase the quality and yield of biogas, in the world practice various bioload additives are used: vegetable waste, clay minerals, and a large amount of the protein-containing waste. The goal – to evaluate the impact of biochar on biogas quality and yield using sewage sludge load. It was found, that 10% biochar additive increased average CH4 concentration of 7.9%, reduced the CO2 concentration of 3–4% and totally removed H2S from biogas.

Overall effect of carbon production and nutrient release in sludge holding tank on mainstream biological nutrient removal efficiency

ABSTRACTThe potential of hydrolysis/fermentation of activated sludge in sludge holding tank (SHT) to produce additional carbon for the biological nutrient removal (BNR) process was investigated. The study was conducted in anaerobic batch tests using the BNR sludge (from a full-scale Westside process) and the mixture of BNR sludge with conventional non-BNR activated sludge (to have higher biodegradable particulate chemical oxygen demand (bpCOD) in sludge). The BioWin 4.1 was used to simulate the anaerobic batch test of the BNR sludge. Also, the overall effect of FCOD production and nutrient release on BNR efficiency of the Westside process was estimated. The experimental results showed that the phosphorous uptake of sludge increased during hydrolysis/ fermentation condition up to the point when poly-P was completely utilized; afterwards, it decreased significantly. The BioWin simulation could not predict the loss of aerobic phosphorous uptake after poly-P was depleted. The results showed that in the case of activated sludge with relatively higher bpCOD (originating from plants with short sludge retention time or without primary sedimentation), beneficial effect of SHT on BNR performance is feasible. In order to increase the potential of SHT to enhance BNR efficiency, a relatively low retention time and high sludge load is recommended.

Microbiota of anaerobic digesters in a full-scale wastewater treatment plant

AbstractAnaerobic digestion is an important technology for the bio-based economy. The stability of the process is crucial for its successful implementation and depends on the structure and functional stability of the microbial community. In this study, the total microbial community was analyzed during mesophilic fermentation of sewage sludge in full-scale digesters.The digesters operated at 34–35°C, and a mixture of primary and excess sludge at a ratio of 2:1 was added to the digesters at 550 m3/d, for a sludge load of 0.054 m3/(m3·d). The amount and composition of biogas were determined. The microbial structure of the biomass from the digesters was investigated with use of next-generation sequencing.The percentage of methanogens in the biomass reached 21%, resulting in high quality biogas (over 61% methane content). The abundance of syntrophic bacteria was 4.47%, and stable methane production occurred at a Methanomicrobia to Synergistia ratio of 4.6:1.0. The two most numerous genera of methanogens (about 11% total) wereMethanosaetaandMethanolinea, indicating that, at the low substrate loading in the digester, the acetoclastic and hydrogenotrophic paths of methane production were equally important. The high abundance of the orderBacteroidetes, including the classCytophagia(11.6% of all sequences), indicated the high potential of the biomass for efficient degradation of lignocellulitic substances, and for degradation of protein and amino acids to acetate and ammonia.This study sheds light on the ecology of microbial groups that are involved in mesophilic fermentation in mature, stably-performing microbiota in full-scale reactors fed with sewage sludge under low substrate loading.

Enhanced methane production and wastewater sludge stabilization of a continuous full scale thermal pretreatment and thermophilic anaerobic digestion

A continuous full scale thermophilic anaerobic digestion (AD) of wastewater sludge in conjunction with thermal pretreatment was developed for enhanced CH4 production as well as sludge stabilization and reduction. Continuous thermal sludge treatment obtained 45.5, 51.7, and 26.1% of hydrolysis based on TS, VS, and COD at 160°C for 30min. After AD, TS, VS, and COD removal efficiencies reached 54.7, 60.4, and 59.2%, respectively, at 3.50kgVS/m3·d. Maximum CH4 yield (0.35m3 CH4/kg VSadd) was obtained at 2.49kgVS/m3·d and less, and the yield decreased with increasing sludge load while net available energy production increased. Continuous thermal sludge treatment and thermophilic AD enhanced CH4 production and solids reduction and showed stable performance for full scale application.

Illumina sequencing for the identification of filamentous bulking and foaming bacteria in industrial activated sludge plants

In this study, Illumina sequencing was used for the identification of bulking and foaming bacteria in industrial wastewater treatment plants. The reliable identification of bulking and foaming bacteria represents the first step in developing effective and specific control strategies to avoid disturbances in activated sludge systems. Illumina sequencing revealed 432 16S rRNA operational taxonomic units, representing phylotypes and including 21 bulking and foaming bacteria in the two investigated industrial wastewater treatment plants. Foaming represents the most severe problem in the cascade biology system. Up to 22.5% of all sequencing reads are bulking and foaming bacteria, including Chryseobacterium, Candidatus Microthrix parvicella and Gordonia sp. as the dominant bulking and foaming bacteria which are known for foam formation. Moreover, Illumina sequencing revealed an increase in Candidatus Microthrix parvicella and Gordonia sp. reads from activated sludge to foam and scum samples, indicating a preferred flotation and/or growth advantages in the foam and scum layers. Analyses of the taxonomic assignment and distribution showed that the phylum Actinobacteria is the most dominant phylum, underlining the key role of Actinobacteria in bulking and foaming. Multivariate data analysis was applied, revealing that the dominant bulking and foaming bacteria are positively correlated with the sludge age and influent flow and negatively correlated with the dissolved oxygen level and the temperature. In terms of developing a specific control strategy, the positive linear relationships to the fatty acid and surfactant sludge loadings are highlighted and the removal of lipid compounds from the wastewater influent could avoid an overgrowth of bulking and foaming bacteria.

Conversion Mechanisms of Carbon, Nitrogen, and Phosphorus in Ozone-Fixed-Bed and Membrane Bioreactors for Deep Treatment of Municipal Tail Water

An ozone-oyster shell fixed-bed bioreactor (OFBR) and a membrane bioreactor (MBR) were constructed and operated for about half a year for the deep treatment of municipal tail water. Pilot-scale test results showed that the combined OFBR-MBR had high removal efficiencies for carbon, ammonium, and phosphorus, and mean removal efficiencies for chemical oxygen demand, ammonium, total nitrogen, and total phosphorus (TP) were 75%, 99%, 20%, and 40%, respectively. Refractory organics in the municipal tail water were transformed to biodegradable organics in the OFBR, and the MBR effectively intercepted the surplus micro-molecular organics and microbes. Ammonium was mostly converted to nitrate, ∼10% of which was released as nitrogen gas through nitrification and denitrification by commonly known aerobic ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and denitrifying bacteria in the OFBR-MBR. The sludge was enriched in TP, which could be removed via surplus sludge discharge when sludge loading increased to overload amounts. Total removal depended on the uptake of phosphorus-accumulating organisms in the aerobic phase. Conversion mechanisms of carbon, nitrogen, and phosphorus in the OFBR-MBR system might be further adjusted to optimize process operation parameters, which might result in greater application of this system.

Synthesis and characterization of drinking water treatment plant sludge-incorporated Portland cement

Kinetic analysis of thermally activated phase transformations in drinking water treatment plant (DWTP) sludge suggests its applicability in the materials of construction. The suggested prediction has already been verified on the sludge-based bricks. The present study deals with incorporating the same sludge in the raw meal for the synthesis of Portland cement clinkers. For this purpose, two raw meals are prepared with varying sludge loadings. The sludge effect on reactivity of the crude mixture is evaluated on the basis of the free lime content sintered at various elevated temperatures. The results of chemical and mineralogical and scanning electron microscopic analyses reveal fine mineralogical contents of Portland clinkers calcined at 1450 and 1500 °C. Moreover, the cements prepared from these clinkers by the introduction of certain proportions of gypsum, depict significant durability. The obtained results elucidate that the studied DWTP sludge-incorporated Portland cement shows considerable potential to be commercialized.

Impacts of electron donor and acceptor on the performance of electrotrophic denitrification.

Electrotrophic denitrification is a novel nitrogen removal technique. In this study, the performance and the mechanism of electrotrophic denitrification were investigated at different nitrate concentrations and current intensities. The results showed that the performance of electrotrophic denitrification was good with a sludge loading of 0.39kg N/kg VSSday. The half-saturation constant for nitrate-N was 1894.03mg/L. The optimal nitrate-N concentration and current intensity were 1500mg/L and 20μA, respectively. Electrotrophic denitrification was defined as the process of direct use of electron for nitrate reduction, and electrotrophic denitrifier was proposed to be the microbe of using electricity as energy source directly. The present work will benefit the development and application of electrotrophic denitrification. Graphical abstract ᅟ.

Bacterial diversity and population shifts driven by spotlight wastewater micropollutants in low-temperature highly nitrifying activated sludge

In this study the influence of low-temperature (8°C), sludge retention time (SRT) and loading of spotlight wastewater micropollutants (MPs) on bacterial community of activated sludge was investigated with a special focus on nitrification. Two Sequencing batch reactors (SBR) and two membrane bioreactors (MBR) were operated with synthetic municipal-like wastewater receiving and not receiving ibuprofen, diclofenac, estrone and 17α-ethynylestradiol (EE2). Bacterial population studies were related to removal efficiencies of studied MPs. The results showed that studied bacterial communities significantly differed from all previously published nitrifying activated sludge communities. Exceptionally low concentration of autotrophic nitrifying bacteria were found (<0.5%) as well as no common heterotrophic nitrifies were presenting in activated sludge and therefore could not be related to the MPs removal. Additionally SRT had a spacious effect on the diversity of bacteria and bacterial population shifts under pressure of MPs. Growth of Firmicutes was suppressed by presence of MPs in all the reactors. Increase of MPs concentrations in wastewater improved the removal of EE2. Abundance of Delta- and Gammaproteobacteria showed positive correlation with diclofenac removal.