Waste Activated Sludge (WAS)

Abstract— A lot of work has been done on the enhancement of lime reactivity by materials containing alumina silicates through pozzolanic reaction. This has lead to investigation of new sources CaO of alumina silicates. Waste Activated Sludge (W.A.S) was found to be enhancing limestone reactivity but to a certain optimum amount, after which it becomes detrimental. Shrinking Core Model (SCM) with mass transfer through the fluid film as the rate-limiting step was compared with chemical reaction as the rate-limiting step. Central cubic design was used for regression analysis of the effects of temperature, lime to W.A.S ratio, liquid to solid ratio and stirring speed in linear, quadratic and interactive aspect. The effects were more pronounced for temperature and least pronounced for stirring speed.

The heat treatment of waste activated sludge was shown to be an effective pretreatment method for anaerobic digestion. Temperatures higher than 180°C lead to the production of recalcitrant soluble organics or toxic/inhibitory intermediates, hence reducing the biodegradability [7]. The only alternative to overcome this drawback is the application of low temperature treatment (< 100°C), and it is suggested as a biological predigestion step as it has an incremental effect over biogas production under thermophilic condition and significantly reduces the energy requirement and formation of refractory intermediates which are seen as a burden in high temperature pretreatments [3]. In thermo- chemical methods, an acid or base is added to solubilize the sludge. NaOH addition in combination with a low temperature (60°C) has led to 51% increase in biogas potential of dairy waste activated sludge [6]. Though pretreatment enhances anaerobic digestion, the latter still suffers practical hindrances such as longer retention time, vulnerability to shock loads etc. An alternative technology is needed to upgrade sludge reclamation and energy conversion. MFC can serve as such an alternative.

Utilization of sewage sludge wastewater treatment plan of crumb rubber industry as adsorbent has not many reported yet. The latest has been reported for metal ion Cr(VI) adsorption with NaOH and H3PO4 activator [31,32]. The present study is aim to characterize a Crumb Rubber Industrial Waste Activated Sludge (CRI-WAS) PT Kilang 5 Gunung as low cost and readily available adsorbent for removal of Cd(II) from aqueous solutions that deals with a series of batch adsorption experiments to investigate and explore the feasibility of an adsorbent. Effect of different parameters such as initial pH, adsorbent dosage, and contact time on the adsorption of Cd(II) have been investigated. Experimental data were fitted to various isotherm equations to determine the best isotherm to correlate the experimental data.

As a byproduct of domestic (sewage) and industrial wastewater treatment plants, waste activated sludge (WAS) is pervasive. WAS is comprised of different groups of microorganisms, organic and inorganic matter agglomerated together in a polymeric network formed by microbial extracellular polymeric substances (EPS) and cations [1]. Treating and then disposing of WAS is costly and can negatively impact the environment. Anaerobic digestion, in which microorganisms are used to breakdown organic matter in the absence of oxygen, is commonly used to stabilize and reduce the volume of the WAS. In the final stage of anaerobic digestion, a methane-rich biogas is produced which can be collected and later used as fuel. The time it takes for anaerobic digestion to reach completion can be as high as 20

Inoculum was collected from a food waste digester (Dufferin Source Separated Organics, Toronto, Ontario, Canada) operating at a solids retention time (SRT) of 30 days. The FW samples were collected from the Grind2Energy (InSinkErator, Racine, WI) system that was used to process FW from grocery stores and transform it to a slurry after grinding. The FW slurry samples were stored in a cold room (4 ºC) and were grinded using a blender for 15 min for homogenization. Similarly, PS and TWAS were collected from the Adelaide pollution control plant (London, Canada). Due to the small size of the port, raw inoculum, primary sludge (PS), thickened waste activated sludge (TWAS), and FW was screened using mesh strainer (1.7 mm) to remove big particles. However, due to the loss of solids and COD through screening, the screened PS and TWAS were concentrated through centrifuging and decanting supernatants to increase COD levels and prepare different feeds, for the designated organic loading and solids retention time of the system.

been investigated with varying degrees of success (Mayhew et al., 2003). Elliott & Mahmood (2007) showed that digester receiving sonicated waste activated sludge (WAS) removed 11%-39% more SCOD than the digester received unsonicated WAS. The aforementioned study also observed that sonication pre-treatment enhanced the destruction rate of volatile solids (VS) by up to 54%. Sonication pre-treatment also improved the gas production by 17% with a 6.2% increase total solids destruction (Muller et al., 2005). Compared to mesophilic digestion, thermophilic digestion has some positive outcomes since biochemical reaction rates are faster, increasing solids and pathogenic reduction, and improved dewatering (Appels et al., 2008). Among with the various pre-treatment technologies, thermal pre-treatment was noted as an effective method since it disrupts the chemical bonds of the cell wall and membrane, thus solubilizing the cell components. Moreover, thermal pre-treatment of WAS showed that soluble COD increased by 25%, 44%, and 60% at 130 0 C, 150 0 C, and 170 0 C, respectively (Elliott et al., 2007). Other pre- treatment technologies like enzymatic hydrolysis can improve biogas by 10% during WAS degradation (Mayhew et al., 2003).

The dewatering of waste activated sludge is one of the most costly and least understood operations in wastewater treatment. While much effort has been put into streamlining operation of sludge dewatering equipment to maximize moisture removal, until recently, little attention was paid to the water within sludge. Sludge water molecules can be subdivided into several categories according to various properties with efforts made to convert sludge water from one category to another with the goal of making it easier to remove. This thesis tests two different ideas. First, that a dewaterability prediction test can be developed that is based on the distribution of moisture within activated sludge. Second, that sludge water can be converted from one form to another thereby improving sludge dewatering.

Xie et al. (2017) state that a recent and notable development in anaerobic digestion is to co- digest two or more substrates together. There are some problems associated with single substrate digestion such as lack of micronutrients, imbalanced C/N ratio, a higher biodegradable fraction etc. These inherent problems can be overcome by co-digestion. Optimal mixture composition between the substrates can be investigated by measuring specific methane production rate. This project aimed to investigate the methane production by the anaerobic co-digestion of food waste, fats, oil and grease, and thickened waste activated sludge. Special emphasis has been made to the percentage of the fats, oil and grease in total substrate as after a certain quantity it inhibits the production of methane (Long et al. 2012).

The model is an electric centrifuge by which a maximum revolutions of 5000rpm could be produced. Its commercial name is Himac CT 6D, Hitachi. Dewatering tube dimensions and radius of revolution are shown in Fig. 4. The tube consists of an outer glassy tube, inner PVC tube, filter paper and filter cloth. The glassy tube fits into an external metallic tube. This external tube has an inner diameter of 4.0cm and is attached to the electrical centrifuge driver. The centrifuge apparatus exposes this tube to a definite number of revolutions using electrical power. These revolutions affect the sludge surface by an equivalent pressure. The pressure produced compresses the sludge and separates the solid particles from water through the filter media. Experiments were carried out to reduce the moisture content of WAS using the flotation process and then exposure to centrifugal force.

The alkaline pretreatment effectively released  ~25  % particle organics (compared to the control) into SCOD (~21  %). A small part of particles (4  %) with reduced TB-EPS (~3  %) were converted into LB COD (~7  %). However, COD contribution was reduced to less than half of SCOD (6–11  %) from particles, when using the freeze/thaw or ultrasonic pretreatment. The SCOD of VFAs reached the peak accumulation during fermen- tation before methane production started, under the conditions of this study [45, 46]. The release of soluble matter also increased conductivity of fermentation solu- tion. Even during fermentation without any pretreat- ment, there was a slight increase from 1.2 to 1.4  mS/ cm in sludge fermentation liquid (SFL) (see Additional file  1: Table S1). Conductivity was further increased to 1.96–2.63  mS/cm by the freeze/thaw and ultrasonic treatment respectively, which matched the increasing trend of SCOD and inorganic ion release. The alkaline addition, using NaOH, highly enhanced the conductiv- ity, reaching up to 6.23 mS/cm, which was almost close to 50 mM PBS (Phosphate buffer solution, pH 7.0) used for MEC reactor setup [35]. A high conductivity is to be considered potentially beneficial to electron trans- port in the following bioelectrochemical process [47]. Besides the additional alkaline contribution, organics and ion release from WAS improves during the pretreat- ment and is further enhanced during the fermentation. A previous study showed that the limiting factors, at the anodic biofilm, change from potential limitations at low conductivity, to dual potential and carbon source trans- fer limitations at a moderate conductivity, and to only mass transfer limitations at high conductivity [48]. A low conductivity (<1 mS/cm) was observed in common AD effluent after organic removal and biological treatment, moreover, a higher external voltage was required when connecting BES after AD to achieve biofuels [49]. In this respect, pretreatment is an important and flexible tool to regulate the performance of BES and AD integrated process, which would determine the total efficiency on waste treatment and biofuel recovery.

Degradation of the highly organic polymers represents the first and overall rate-limiting step for the mineralization of organic matter in activated sludge and anaerobic digested sludge treatment systems [59-61]. In our work, the studied pretreatment involved alteration of pH, which is an im- portant parameter affecting both bacterial activity and me- tabolite pathways. KO-based annotations were used to understand how these phylogenetic trends could be used to predict the metabolic potential of these microbes. Figure 5 shows the subsystems that are related to higher methane production, including metabolism of amino acids, energy, carbohydrates, nucleotides, lipids, cofactors and vitamins, xenobiotics, as well as the fermentation of different substrates. These results revealed a general ele- vated expression of these faculties in the bioreactors fed with un-pretreated sludge over time (compare UP30 and UP40), whereas these levels were highest in the bioreactor digesting pretreated sludge (P30). Distribution of the func- tional systems was most divergent in P30, which showed predominance in metabolism consistent with a commu- nity shifted towards an enhanced biomass degradation metabolism. Herewith, the downstream analysis focused on the degradation of carbohydrates for a number of rea- sons. Firstly, the matrix of extra-cellular polymeric sub- stances (EPS) that crosslink cells together remains the primary solid part of biological sludge, of which the poly- saccharide is the predominant component [62-64]. Sec- ondly, complex carbohydrate is the commonplace recalcitrant in the hydrolysis process, and bioprospecting Table 2 Relative abundance of Archaea in pretreated and un-pretreated sludge bioreactors at day 30 and 40

In addition, since only the FOG component of GI/GT is refinable for biodiesel production, converting FOG waste into biodiesel leaves the remaining waste disposal of food residuals and wastewater a challenge. A BlackGold Biofuels’ 250k FOG-toFuel® system was proposed for a FOG-to-biodiesel installation at Missouri Bissell Point WWTF ( Missouri Department of Natural Resources, 2011 ) . The system includes (a) a dewatering process to remove water portion from inlet FOG waste streams (GIW/GTW, grease from dissolved air flotation unit at WWTFs, and scum from internal WWTF processes), and (b) a chemical conversion and purification process to convert the processed dry FOG into biodiesel. It is clear that processing FOG wastes into dry grease and eventually biodiesel is feasible with proper pretreatment and chemical reaction process, but often comes with the generation of liquid and solid waste byproducts as new waste streams.

Rigorous monitoring of parameters was also performed intensively. For the first two feedings, biogas production and methane content were monitored every 6 hours following the first perturbation. In that same time interval, a total volume of 15-30 mL of anaerobic sludge was also drawn from both reactors, to measure its pH and volatile fatty acids (VFA), as well as DNA extraction for future molecular studies. The pH was measured immediately right after collecting the effluent, while sludge for VFA samples were pre-treated first and collected in batch before being analyzed with the help of David C. Black using Shimadzu GC-FID in Environmental Engineering Lab. This sample collection, however, eventually resulted in the decrease of sludge volume in the reactor, though the volume removed every time samples were drawn was insignificant. During the test, the volume inside reactors fluctuated between 5.9 and 6 liters depending on the frequency of sample collection. The next feeding time would then compensate the deficit of sludge volume inside the reactor by adding extra amount of the same feedstock.

93 Therefore, the objectives of this study were a to compare the short term effects and fate of CuO 94 NPs and Cu2+ in a laboratory scale waste activated sludge process fed with real was[r]

Biomethane production from processed industrial food waste (IFW) in admix- ture with sewage sludge (primary and waste activated sludge: PS and WAS) was evaluated at a range of C:N ratios using a standard biochemical methane potential (BMP) test. IFW alone had a C:N of 30 whereas for WAS it was 5.4 and thus the C:N ratio of the blends fell in that range. Increasing the IFW content in mix im- proves the methane potential by increasing both the cumulative biogas production and the rate of methane production. Optimum methane yield 239 mL/g VSre- moved occurred at a C:N ratio of 15 which was achieved with a blend containing 11 percent (w/w) IFW. As the fraction of IFW in the blend increased, volatile solids (VS) destruction was increased and this led to a reduction in methane yield and amount of production. The highest destruction of volatile solids of 93 percent was achieved at C:N of 20 followed by C:N 30 and 15. A shortened BMP test is adequate for evaluating optimum admixtures.

anaerobic digestion process. From an economic and environmental perspective, the enhanced methane production was of great significance because not only could higher renewable energy be generated in wastewater treatment plants, but methane emission into the atmosphere, as a major greenhouse gas, could decline considerably from sludge treatment units, responsible for the production of 50% of total greenhouse gas emission of wastewater treatment plants (Pilli et al., 2016). The amount of methane produced in the system by means of single hydroxide or thermal pre-treatment was consistent but slightly higher than the methane production, obtained in previous studies, further confirming the effectiveness of hydrogen peroxide and thermal pre- treatment when enhancing anaerobic digestion of sewage sludge (Wang et al., 2014; S. Zhang et al., 2015; T. Zhang et al., 2015). Zhang et al. (2015) revealed that pre-treatment of waste activated sludge with 50 mg H 2 O 2 /g TS for 24 hours can enhance

The amount of time that solids expend on the bottom of the secondary clarifier is a function of the RAS pumping rate. The settled microorganisms and solids are in a embitter condition as long as they remain in the secondary clarifier. If sludge is allowed to remain in a secondary Separator too long it will begin to float to the surface of the clarifier due to nitrogen gas assert during the biological process ofde- nitrification (rising sludge)[9], [10]. Monitoring and controlling the depth of the sludge blanket in the secondary Separator and the concentration of solids in the RAS are significant for the proper operation and control of the activated sludge system. A sludge settle-ability test, known as a settle meter, can be used to indication the rate of sludge settling and compaction. This information is used to detest appropriate RAS pumping rates. Typically, RAS pumping rates of between 25% and 150% of the influent flow are commonly used. Measuring the solids concentration of RAS allows the return volume to be regulated to keep the solids level in the aeration basin within the control parameters. Excess sludge which eventually cumulates beyond that rebounded is specified as Surplus or Waste Activated Sludge (SAS/WAS). This is removed from

Phosphor, Nitrogen, Carbon and Oxygen are required that were added every day. In the starting test, first and second day the sludge settling time was two hours then collected the dead cells. On the third day sludge feeding began. The amount of feed was equal to glucose 7.5 g/day, Ammoni- um phosphate 0.34 g/day and Ammonium nitrate 0.93 g/day. The feeding was done for a week. So the culture was ready for testing.

Sürücü and Dilek ( 1989) reported that at DO concentration < 2.0 mg/l turbid effluent were obtained. They reported the cause to be due to the inhibition of Eucaryotes population. Another cause was that low DO concentration inhibits the production of exocellular polymers, which function during bio-flocculation. They also reported that zone settling velocities could not be determined at low DO levels (0.5, 1.0, 1.5 mg/l) because the flocculation of microorganism was not good. The mixed liquor was blackish and interface fall with respect to time could not be recorded. On the other hand, at high DO concentration (2.0 and 5.0 mg/l), microorganisms were well flocculated; cultures were lighter in color and the sludge settled without leaving high effluent turbidity with a distinct interface. They reported zone-settling velocities of 9.63 m/hr and 9.36 m/hr at DO levels of 2.0 mg/l and 5.0 mg/l respectively for MLSS of 3000 mg/l. Therefore, the settleability of activated sludge is not improved by the increasing the DO concentration from 2.0 to 5.0 mg/l. At higher DO concentration the flocs were bigger and non- dispersed, turbidity was low and the settlement was observed. Sludge volume indices were measured and it was observed that SVI values at 2.0 and 5.0 mg/l of DO concentration did not differ from each other appreciably.

Abstract The aim of this study is to investigate the usability of sewage sludge, a waste from waste water treatment facility, at constant temperature and different pH conditions in the hydrogen production by dark fermentation. It was understood from the results that hydrogen production varies according to the characterization of activated sludge. In the experiments performed at different pH values (pH 4-8) at 35°C, maximum hydrogen production was achieved within the first 24 hours. Except for one performed at pH 8, hydrogen gas release was observed at other pH values within 2 hours. However, according to the results obtained at the 24th hour, maximum hydrogen production (2489 mL/m 3 H