Influence of Pyrolytic Biochar on Settleability and Denitrification of Activated Sludge Process

Biochar is a massively produced by-product of biomass pyrolysis to obtain renewable energy and has not been fully used. Incomplete separation of sludge and effluent and insufficient denitrification of sewage are two of main factors that influence the efficiency of activated sludge process. In this work, we proposed a new utilization of biochar and investigated the effect of biochar addition on the performance of settleability and denitrification of activated sludge. Results show that the addition of biochar can improve the settleability of activated sludge by changing the physicochemical characteristics of sludge （e.g., flocculating ability, zeta-potential, hydrophobicity, and extracellular polymeric substances constituents）. Moreover, the dissolved organic carbon released from biochar obtained at lower pyrolysis temperature can improve the nitrate removal efficiency to a certain extent.

Ammonium Ion Adsorption and Settleability Improvement Achieved in a Synthetic Zeolite-Amended Activated Sludge

Municipal wastewater treatment plants typically exhibit two classic problems： high ammonium concen- tration in water after conventional biological treatment and, in some cases, poor activated sludge sediment ability. Potential solutions to these problems were investigated by adding a synthetic zeolite obtained from coal fly ash to different steps of activated sludge treatment. The experimental results for ammonium removal fit well with the theoretical adsorption isotherms of the Freundlich model with a maximum adsorption capacity of 13.72 mg.g-＇. Utiliza- tion of this kind of zeolite to improve activated sludge sediment ability is studied for the first time in this work. It is found that the addition of the zeolite （1 g. L-1） to an activated sludge with settling problems significantly enhances its sediment ability and comoact ability. This is confirmed by the sludge volume index （SVI）, which was reduced from 163 ml.g-1 to 70 ml.g-r, the V60 value, which was reduced from 894 ml.L-1 to 427 ml.L-1, and the zeta poten- tial （0, which was reduced from -19.81 mV to -14.29 mV. The results indicate that the addition of this synthetic zeolite to activated sludge, as an additional waste management practice, has a positive impact on both ammonium removal and sludge settleability.

Effects of low temperature on sludge settleability and nutrients removal performance treating domestic wastewater

In order to investigate the effect of temperature on activated sludge systems,sludge settleability,nitrogen and phosphorus removal processes were investigated by changing temperature variation patterns using 4 sequencing batch reactors (SBR).The results showed that no matter temperature changes in the range of 15-22 ℃ (decrease or increase) gradually or sharply,it has little effect on nitrogen and phosphorus removal processes.But when temperature decreases to 12 ℃,biochemical reactions will be inhibitted obviously.At least 1 sludge retention time (SRT) is needed for nitrification adapt to new temperature envirionment,and more time is necessary for phosphorus removal process.When temperature increases from 12 ℃ to 22 ℃ sharply,nitrification process deteriorates seriously,but phosphorus removal process shows no change.In addition,sludge settleability deteriorates when temperature changes sharply (decrease or increase),but the reasons are different.Under temperature decrease condition,it is mainly caused by the increase of accumulated extracellular polymeric substances (EPS).Under temperature increase condition,the loosing sludge flocs' configuration is the main reason.It should be pointed out that the filamentous bacteria content during the entire experiment keeps almost constant,and the sludge settleability variations are the reflection of the change of sludge physicochemical characteristics.

Influence of Na^+,K^+,Mg^(2+),Ca^(2+),and Fe^(3+) on filterability and settleability of drilling sludge

Solid–liquid separation is a vital step in drilling sludge disposal, and the filterability and settleability of drilling sludge are the main evaluating indicators for the separation process. The influence of Na^+,K^+,Mg^(2+),Ca^(2+),and Fe^(3+) on drilling sludge filterability and settleability was investigated in our research. The water content,filtration rate, supernatant volume and supernatant turbidity were measured to evaluate the filterability and settleability of drilling sludge. Meanwhile, the zeta potential, specific surface area of sludge flocs, particle size distribution and Fourier-transformed infrared spectra were employed to clarify the influencing mechanism.The experimental results showed that the filterability and settleability of drilling sludge were related to concentration and types of cations. Mg^(2+),Ca^(2+),and Fe^(3+) performed better than Na^+, K^+, and the cations with smaller hydrated radius got superior solid–liquid separation behavior at same valence. Finally, the spectra indicated that no chemical adsorption occurred between inorganic cations and drilling sludge flocs. The variation of surface charge and flocs growth after adding different inorganic cations were the reasons for the changes of the filterability and settleability.

Characteristic of COD removal and sludge settleability in biological treatment of hypersaline wastewater

In order to investigate the feasibility of biological treatment of bypersaline wastewater produced from toilet flushing with seawater at low temperature, pilot-scale studies were established with plug-flow activated sludge process at low temperature （5-9℃） based on bench-scale experiments. The critical salinity concentration of 30 g/L, which resulted from the cooperation results of the non-halophilic bacteria and the halophilic bacteria, was drawn in bench-scale experiment. Pilot-scale studies showed that high COD removal efficiency, higher than 85 %, was obtained at low temperature when 30 percent seawater [ seawater/（seawater ＋ sewage） ] was introduced. The salinity improved the settleability of activated sludge, and average SV dropped down from 38% to 22. 5% after adding seawater. Sludge bulking could be forborne effectively because filamentous bacteria couldn＇t subsist under high salinity concentration.

Relationship between sludge settleability and membrane fouling in a membrane bioreactor

The evolution of activated sludge settleability and its relationship to membrane fouling in a submerged mem-brane bioreactor were studied at a lab-scale equipment fed with synthetic wastewater.It was found that sludge volume index(SVI)gradually increased and the sludge settleability was reduced,which was caused by the propagation of filamentous bacteria.With increasing SVI,the average increasing rate of trans-membrane pressure increased,the stable filtration period was shortened,and the two stages(smooth stage and accelerating stage)of the trans-membrane pressure were more obvious.At the same time,the increasing rate of trans-membrane pressure at the smooth stage decreased and the rate at the accelerating stage increased with SVI,respectively.The observation by using scanning electronic microscopes showed the cake layer with loose structure and large thickness formed on the membrane surface due to the appearance of filamentous bacteria and high SVI in sludge.Influence of the sludge settleability on the trans-membrane pressure was related to the structure and thickness of the cake layer on the membrane.

Control of sludge settleability and nitrogen removal under low dissolved oxygen condition

Low dissolved oxygen （DO） is an energy- saving condition in activated sludge process. To investi- gate the possible application of limited filamentous bulking （LFB） in sequencing batch reactor （SBR）, two lab-scale SBRs were used to treat synthetic domestic wastewater and real municipal wastewater, respectively. The results showed that prolonging low DO aeration duration and setting pre-anoxic （anaerobic） phase were effective strategies to induce and inhibit filamentous sludge bulking, respectively. According to the sludge settleability, LFB could be maintained steadily by adjusting operation patterns. Filamentous bacteria content and sludge volume index （SVI） were likely correlated. SVI fluctuated dramatically within a few cycles when around 200 mL-g~, where altering operation pattern could change sludge settleability in spite of the unstable status of activated sludge system. Energy consumption by aeration reduced under low DO LFB condition, whereas the nitrification performance deteriorated. However, short-cut nitrification and simultaneous nitrification denitrification （SND） were prone to take place under such conditions. When the cycle time kept constant, the anoxic （anaerobic） to aerobic time ratio was determining factor to the SND efficiency. Similarity keeping aerobic time as constant, the variation trends of SND efficiency and specific SND rate were uniform. SBR is a promising reactor to apply the LFB process in practice.

Interplay Factors Involved in the Inadequate Performance of Four Activated Sludge Systems in Northern Gauteng-South Africa

A recent study conducted on the four activated systems serving the surrounding communities in the Northern Gauteng revealed the failure of three of these wastewater treatment plants to remove enteric pathogenic bacteria and protozoan parasites such as Cryptosporidium and Giardia spp. To determine the factors involved in the inadequate performance of the plants, the following parameters were considered： the design characteristic of the plants, the microbiological structure and the physical characteristics of the plants. The results revealed that higher than optimal influent loadings and inadequate aeration systems, observed in Baviaanspoort, Refilwe and Rayton Water Care Works （WCW） increased the composition of filamentous bacteria in flocs and decreased the diversity of protozoan species in the sludge. Sequentially, these resulted in the poor settling properties of the sludge at these plants. However, Zeekoegat WCW showed optimum influent loads and adequate aeration systems. This maintained balance in the microbial community, resulting in good clarification of the sludge.

Innovative method of culturing bdelloid rotifers for the application of wastewater biological treatment

This study aims to establish a simple and efficient method for the mass culture of bdelloid rotifers,which is the basis for the application of bdelloid rotifers as biological manipulators to improve wastewater biological treatment performance.A common bdelloid rotifer,Habrotrocha sp.,in a wastewater biological treatment system was selected as the culture target.Rotifers fed on flour could reproduce faster than those fed traditional food such as Chlorella vulgaris or mixed bacteria.As a rotifer food,flour has the advantages of simple preparation,effortless preservation,and low cost compared to live Chlorella vulgaris or mixed bacteria,so it is more suitable for the mass culture of rotifers.The optimal rotifer culture conditions using flour as food were also studied.According to the experimental results,the recommended rotifer culture conditions arc a flour particle size of 1 a flour concentration of 6×10^(6) cell/mL,a temperature of 28℃,a pH level of 6.5 and salinity of 100-500 mg/L.In addition,the sludge volume index in the sequencing batch reactor(SBR)with the addition of cultured rotifers was 59.9 mL/g at the end of operation and decreased by 18.2%compared to SBR without rotifer,which indicates that the cultured rotifers still retained the ftinction of helping to improve sludge settling.This function may be related to the rotifer's role in inhibiting bacteria from producing loosely bound extracellular polymeric substances in the SBR.