Volatile fatty acids production from fermentation of secondary sewage sludge : a thesis presented in partial fulfillment of the requirements for the degree of Master of Engineering in Environmental Engineering

Sludge fermentation is used worldwide as an economical means to produce volatile fatty acids (VFA), which can be used as readily available carbon in biological nutrient removal (BNR) systems. In this research, secondary sludge was tested for its potential to generate VFA. Fermentation of secondary sludge was carried out in a lab-scale sequencing batch reactor (SBR). The SBR was fed with secondary sludge of 1% total solids and run with hydraulic retention time (HRT) of 48 hours and 28 hours in phase 1 (40 days) and phase 2 (12 days) respectively. The SBR produced net VFA (expressed as acetic acid) of 365 ±62.5 mg VFA HAC /I which was equivalent to a VFA yield of 0.28 ±0.05 mg VFA HAC /mg VSS feed during phase 1. A change in operating HRT from 48 hours to 28 hours led to a reduction in solids retention time (SRT) from 2.65 days to 2 days in phase 2. The reduction in SRT during phase 2 led to poor hydrolysis and hence could not support the fermentation. Net VFA generation decreased during phase 2 and reached 0 mg/I. Acetic acid was the main acid produced comprising 45% of total VFA content during the run with 48 hours HRT. The effect of total solids (TS) concentration on secondary sludge fermentation was tested using batch experiments. The batch with 2.8% TS secondary sludge showed a maximum net VFA production of 60 mg VFA HAC /I, which appeared to be superior to the 1% TS secondary sludge batch fermentation where no net VFA production observed throughout the test period. Primary sludge (3% TS) exhibited 1200 mg VFA HAC /I in a batch fermentation, which was superior to the net VFA produced during secondary sludge (2.8% TS) batch fermentation. The effects of sonication on fermentability of primary and secondary sludges were tested. A sonic power application of 0.0017 Watt/ml/min density increased soluble content of primary and secondary sludges. In batch fermentations, sonicated secondary sludge improved fermentation over unsonicated secondary sludge. A maximum net VFA production of 130 mg VFA HAC /I was observed in the secondary sludge batch fermentation. In this research work, an investigation into inhibiting VFA degradation in secondary sludge batch fermentations was also carried out. The effects of a methanogenic bacteria inhibitor (bromoethane sulfonic acid) and low pH (range of 4.02-6.07) were considered. The addition of 1 mM bromoethane sulfonic acid (BES) in secondary sludge (1% TS) batch fermentation successfully inhibited VFA degradation. pH values as low as 4.02 showed an inhibitory effect on secondary sludge (1% TS) batch fermentation which led to poor hydrolysis and hence no net VFA generated during the test period. However, low pH values reduced the VFA degradation rate in the batch fermentations. Secondary sludge used in the present research showed the potential to generate VFA. The amount of VFA produced in the present work showed the potential to improve the performance of a BNR system. Moreover, in batch fermentations, VFA generation was improved using various pre-treatments like sonication and BES addition

Full-scale combination of anaerobic digestion and concentration by evaporation in Garrigues (Lleida, Spain): evaluation after 2 years of operation

Evaporation process is a reliable strategy to manage pig slurry, removing water and recovering nutrients by concentration. The described treatment plant, TRACJUSA, applies the VALPURENTM process, which is based on the combination of anaerobic digestion and evaporation. The benefits of this combined process have been previously reported at laboratory scalePostprint (published version

In Vitro Rumen Fermentation and Anti Mastitis Bacterial Activity of Diet Containing Betel Leaf Meal (Piper Betle L.)

The aims of this experiment was to study the inhibition effect of betel leaf meal (BLM) addition into concentrate diet on mastitis causing bacteria and on rumen fermentation condition. The study consisted of five dietary treatments of BLM level in concentrate feed, i.e., 0%, 2%, 4%, 6%, and 8% and four replicates of each treatment. The treatment diets together with napier grass in ratio of 40 : 60 were fermented using rumen liquor. All treatments were examined their antibacterial activity before and after fermentation. After four hours fermentation, supernatant of each samples were analyzed for VFA, NH3, number of bacteria and protozoa. Dry matter (DM) and organic matter (OM) digestibility were analyzed after 48 h fermentation. The results showed that before fermentation, 8% BLM addition caused the bigest (P<0.05) inhibition diameter of Staphylococcus spp. growth compared to other lower levels. However after fermentation there were no significant differences among the addition levels of BLM. Two per cent of BLM addition produced higher VFA (P<0.05) than the other addition levels. Ammoniaconcentration, dry matter (DM) and organic matter (OM) digestibility were not different among the treatments. Addition of BLM significantly (P<0.01) decreased protozoa number, but did not affect bacterial count. It is concluded that the addition of 2% BLM in concentrate feed can be used effectively to inhibit the growth of mastitis causing bacteria (Staphylococcus spp.) and does not disturb rumen fermentation condition

Optimization of the anaerobic co-digestion of pasteurized slaughterhouse waste, pig slurry and glycerine

The feasibility of co-digestion of blends of two different animal by-products (pig manure and pasteurized slaughterhouse waste) and recovered glycerine was studied in mesophilic conditions. Experiments were performed in a lab-scale CSTR along 490 days, with a hydraulic retention time of 21–33 days and with a step-wise increased organic loading rate, by adding and/or changing the wastes ratio, from 0.8 to 3.2 kgCOD m-3 d-1. The best methane production rate (0.64 Nm3CH4 m-3 d-1) represented an increment of 2.9-fold the initial one (0.22 Nm3CH4 m-3 d-1 with pig manure solely). It was attained with a ternary mixture composed, in terms of inlet volatile solids, by 35% pig slurry, 47% pasteurized slaughterhouse waste and 18% glycerine. This blend was obtained through a stepwise C/N adjustment: this strategy led to a more balanced biodegradation due to unstressed bacterial populations through the performance, showed by the VFA-related indicators. Besides this, an improved methane yield (+153%) and an organic matter removal efficiency (+83%), regarding the digestion of solely pig slurry, were attained when the C/N ratio was adjusted to 10.3.Postprint (author's final draft

Co-digestion of the mechanically recovered organic fraction of municipal solid waste with slaughterhouse wastes

The current work aimed to resolve some long-standing questions about the potential benefits and limitations of co-digestion of slaughterhouse wastes. To achieve this, a laboratory-scale trial was carried out using the mechanically recovered organic fraction of municipal solid waste mixed with either sheep blood or a mixture of pig intestines with flotation fat. Both of these co-substrates are difficult to digest in isolation because of their high nitrogen and lipid concentrations, and are regulated as Category 3 materials under the Animal By-Products Regulations (EC 1069/2009). The results showed that at an organic loading rate of 2 kg VS m?3 day?1 with the slaughterhouse material making up 20% of the load on a volatile solids basis the process could operate successfully. As the loading was increased to 4 kg VS m?3 day?1 signs of inhibition appeared with both co-substrates, however, and volumetric methane production was reduced to a point where co-digestion gave no process advantage. The main operational problem encountered was an increase in the concentration of volatile fatty acids in the digestate, particularly propionic acid: this was thought to be a result of ammonia toxicity. The concentration of potentially toxic elements in the digestate made it unsuitable for agricultural application for food production, although the increased nitrogen content made it more valuable as a fertiliser for non-food crop use

Movement-Efficient Sensor Deployment in Wireless Sensor Networks With Limited Communication Range.

We study a mobile wireless sensor network (MWSN) consisting of multiple mobile sensors or robots. Three key factors in MWSNs, sensing quality, energy consumption, and connectivity, have attracted plenty of attention, but the interaction of these factors is not well studied. To take all the three factors into consideration, we model the sensor deployment problem as a constrained source coding problem. %, which can be applied to different coverage tasks, such as area coverage, target coverage, and barrier coverage. Our goal is to find an optimal sensor deployment (or relocation) to optimize the sensing quality with a limited communication range and a specific network lifetime constraint. We derive necessary conditions for the optimal sensor deployment in both homogeneous and heterogeneous MWSNs. According to our derivation, some sensors are idle in the optimal deployment of heterogeneous MWSNs. Using these necessary conditions, we design both centralized and distributed algorithms to provide a flexible and explicit trade-off between sensing uncertainty and network lifetime. The proposed algorithms are successfully extended to more applications, such as area coverage and target coverage, via properly selected density functions. Simulation results show that our algorithms outperform the existing relocation algorithms