Ancheng Luo

Effect of Solid-Liquid Separation on BOD and VFA in Swine Manure

Fresh swine manure was sieved into seven different particle size categories, i.e., <0.075 mm, < 0.15 mm, < 0.25 mm, < 0.5 mm, < 1.0 mm, < 1.4 mm, and < 2.0 mm. Manure was stored in seven PVC columns and sampled every 5 days up to 30 days. Manure samples were analyzed for total volatile fatty acids (VFAs), 5-day biochemical oxygen demand (BOD5), total solids (TS), total suspended solids (TSS), and total volatile solids (TVS). Two parameters (VFAs and BOD5) were used to determine the odor generation potential of the test manure. The results showed that total VFAs correlated well with BOD5 (R 2 = 0.8297). The levels of TSS only explained 40% of BOD5 and 46% of VFAs, both of which increased with storage time, regardless of solid particle sizes. Also, the data inferred that most of the odorous compounds (measured by VFA and BOD levels) were contained in manure solid particles less than 0.075 mm. These cannot be removed by commercial mechanical separators with screen size ranging from 0.5 to 3.0 mm. With an average separation efficiency of 25% for most commercially available mechanical separators, the removal efficiencies of BOD5 and VFAs were as low as 10% and 12%, respectively. These findings cannot justify the use of solid-liquid separation to control odor. Data also showed that for swine manure, it is critical to run separation treatment within the first ten days after the manure is excreted to potentially improve the separation efficiency. After ten days, the degradation of TSS was accelerated due to the increased biological activities, which may greatly reduce the separation efficiency.

Changes in swine manure solids during storage may affect separation efficiency.

A laboratory study revealed the dynamic changes of solids in swine manure during storage in order to determine the best time for efficient solid-liquid separation treatment. Data showed that separation should be conducted within 10 days after manure excretion for particle sizes equal to or greater than 0.5 mm and within five days for particle sizes smaller than 0.5 mm. After the first 10 days of storage, the total suspended solids tended to be decomposed at a higher rate, thus reducing separation efficiency. Particles equal to or smaller than 0.25 mm were biologically decomposed at the same rate without relevance to the particle size during the first 20 days of storage. The level of total volatile solids in liquid manure was linearly correlated with the total solids content with a correlation coefficient of 0.9850 in the 30-day period.

RAISING pH BY LOW–LEVEL AERATION FOR SOLUBLE PHOSPHORUS REMOVAL OF SWINE MANURE

Soluble phosphorus (P) removal by increasing swine manure pH was investigated in this study. Sodium hydroxide (1 M) was used to increase the manure pH from 6.5 to 9. Two aeration treatments (intermittent and continuous) were also used to raise the manure pH from 6.5 to 8.0 (for the intermittent treatment) and from 6.5 to 8.4 (for the continuous treatment) in a period of 15 days. An airflow rate of 1 L/minute was used for both schemes. Results showed that raising the pH to 8 by sodium hydroxide (NaOH) led to a reduction in soluble P concentration by 80%. Increasing the pH above 8 had little effect on further removal of soluble P. For both the intermittent and continuous aeration programs, the manure pH increased by about 1 unit within the first day of experiment, accompanied by a 75% reduction in soluble P concentration in the liquid. The treatment with continuous aeration did not show advantage over the intermittent mode in removing soluble P from liquid swine manure. Therefore, to accomplish the same level of soluble P removal, intermittent aeration should be recommended to save energy.

BACTERIAL RESPONSES TO TEMPERATURE DURING AERATION OF PIG SLURRY

The temperature effect on total anaerobic and aerobic bacterial growth in pig slurry was studied using low level batch aeration treatments. Five bioreactors were built using Plexiglas tubes to perform five temperature treatments (5 °C, 10 °C, 15 °C, 20 °C, and 25 °C). An airflow rate of 0.129 L/min/L manure was used to aerate manure contained in all reactors. Data showed that temperature had a profound impact on the aerobic counts in pig slurry during the aeration process. When the temperature increased from 15 °C to 25 °C, the average oxidation–reduction potential decreased from +40 mV to −60 mV, accompanied by a 75% reduction of aerobic bacteria in the manure. At 25 °C, the anaerobic counts were consistently higher than aerobic counts for most of days. A quadratic relationship was observed between the aerobic counts and the oxidation–reduction potential with a correlation coefficient of 0.8374. To reduce odor generation potential, the oxidation–reduction potential in the manure should be maintained at +35 mV or higher.

Effects of bioreactor temperature and time on odor-related parameters in aerated swine manure slurries.

Abstract Previous studies have linked odor generation from swine manure to some characteristics of the liquid manure such oxidation‐reduction potential (ORP), five‐day biochemical oxygen demand (BOD5), volatile fatty acids (VFAs), and predominant microbial population. This study investigated the effect of bioreactor temperature and time on the aforementioned parameters during aeration of swine manure. Five reactors (13 1 capacity) loaded with swine manure and maintained at temperatures of 5, 10, 15, 20, and 25oC, were supplied with air for 15 days to maintain aerobic conditions. Large fluctuations in ORP (‐120 to 360 mV) were observed in the first seven days of aeration, which stabilized thereafter regardless of the bioreactor temperature. The percentage removal of VFAs and BOD5 in the manure significantly increased from 0.0% on day one to 87.8% and 65.3%, respectively, on day nine, and remained relatively constant thereafter. The mean percentage of VFAs and BOD5 removed also increased significantly with an increase in the bioreactor temperature. The VFAs and BOD5 removal increased by approximately 25% and 35%, respectively, in going from 5 to 25°C, during the 15 days of aeration. Both VFAs and BOD5 in the manure were significantly correlated with ORP, aerobic bacteria, and anaerobic bacteria. The data suggested that continued aeration for seven days at 20 or 25°C was sufficient for significant reduction of odor precursors (VFAs and BOD5) and in stabilization of swine manure. A linear correlation of 0.97 between VFAs and BOD5 indicated that the two parameters can be used interchangeably as indicators of odor release potential in swine manure.

PHOSPHORUS TRANSFORMATIONS IN SWINE MANURE DURING CONTINUOUS AND INTERMITTENT AERATION PROCESSES

The work presented here was to determine the transformation of phosphorus (P) between different forms in the process of intermittent and continuous aeration. According to this study, aeration, at an airflow rate of 1.0 L/min, resulted in an increase in the manure pH of about one unit, from 6.5 to 7.5, within 24 hours, accompanied by a reduction in soluble ortho–P of 76%. This reduction in soluble P was apparently caused by the chemical precipitation that was indicated by a reduction in organic P and a simultaneous increase in insoluble inorganic P. The analysis of mass balances between the P fractions showed a large transformation of inorganic insoluble P into organic forms during the aeration period, which could overshadow the efficiency of soluble P removal by microbes. Because the manure contained about 73.5% insoluble inorganic P, it is suggested that solid–liquid separation should be performed prior to aeration to increase the efficiency of soluble P removal. In addition, continuous aeration did not show an advantage over intermittent aeration in terms of soluble P removal.

THE EFFECT OF LIMITED AERATION ON SWINE MANURE PHOSPHORUS REMOVAL

Two low level aeration schemes (intermittent vs. continuous)were investigated on a laboratory scale, in conjunction with swine manure pH adjustment using sodium hydroxide (1.0 M), for manure phosphorus (P) removal. According to the data, an 80% reduction in soluble P was observed when the manure pH was increased to 8. Both intermittent and continuous aeration treatments could raise manure pH above 8 with an airflow rate of 1 L/minute in a period of 15 days. A drastic increase in pH (about 1 unit) was observed for both aeration schemes within the first day of test, resulting in a 76% reduction in soluble P concentration in the liquid. It appeared that there is no difference in terms of P removal between the two aeration programs, suggesting that the intermittent aeration be preferred to save energy while still achieving the same level of P removal.

Influence of temperature and time on phosphorus removal in swine manure during batch aeration.

This study was conducted to investigate the effects of temperature and time on the mechanisms of phosphorus removal in swine manure during aeration. Removal of soluble orthophosphates significantly increased with aeration time and temperature. Successive significant ortho‐P removals were observed between days one and nine but no significant additional removals were recorded thereafter. Removals were significantly higher at temperatures of 20 and 25°C than at temperatures of 5, 10, and 15°C and ranged between 22.9 to 31.0%. Insoluble inorganic phosphorus also changed significantly with aeration time and temperature and with a similar trend as soluble orthophosphates. The pH of the manure explained 92 and 87% of the content of insoluble inorganic phosphorus at lower temperatures (5, 10, 15°C) and at higher temperatures (20, and 25°C), respectively. Organic phosphorus and aerobes growth patterns were similar to that of soluble orthophosphates removal. The rapid growth of aerobes was most probably the principal factor behind a rapid soluble ortho‐P removal above 15°C. The contribution of inorganic phosphates to the removal of soluble orthophosphates was approximately 61% while that due to organic P was approximately 35%. Precipitation was found to be the principal mechanism governing removal of soluble ortho‐P in swine manure during aeration treatments.

Influence of Anaerobic Pre-conditioning on Phosphorus Removal in Swine Manure by Aeration

A feasibility study with three pre-conditioning times was carriedout to examine the effect of anaerobic pre-treatment on phosphorus removal by aeration. The results showed that solublephosphorus could be decreased from 120 mg L-1 to about40 mg L-1 within one-day aeration. However, soluble phosphorusconcentration was found not affected by pre-conditioning, butmore pH dependent. Anaerobic pre-treatment significantly increased the uptake of phosphorus by microbes indicated by theincrease in concentration of organic phosphorus fraction. The presence of a large proportion of inorganic insoluble phosphorusconsiderably eclipsed the biological removal of soluble phosphorus, which suggested that the solids/liquid separationbefore aeration could be important to improve the biologicaluptake of soluble phosphorus.

EFFECT OF MICROBIAL ADDITIVES COMBINED WITH AERATION ON REDUCTION OF NUTRIENTS IN SWINE MANURE

The research presented in this article evaluated a technique using manure additives (Sporzyme and activated sludge) coupled with aeration treatment in reducing nutrients from liquid swine manure. Plastic columns, 91.6 cm in height and 15.3 cm in internal diameter, were each filled with 15 L liquid swine manure. Aeration was provided to each column by an air pump at an airflow rate of 2.0 L/min, controlled by individual airflow meters mounted on the columns. The experiment included five treatments: (1) control (no aeration and no additives), (2) aeration alone, (3) aeration with a microbial additive (Sporzyme), (4) aeration with activated sludge inoculum without anaerobic incubation prior to aeration, and (5) aeration with activated sludge inoculum with three days of anaerobic incubation prior to aeration. The results indicated that total Kjeldahl nitrogen (TKN), ammonia-N, and total soluble phosphorus were reduced by about 42%, 56%, and 72%, respectively, by all the treatments except the control. The reduction of TKN was found to be mainly attributed to the reduction of ammonia because its share of TKN was remarkably reduced at the end of the test. Although Sporzyme significantly increases the aerobic count in the manure, data from this study have showed no advantage of its use (or the activated sludge as seeding) solely for enhancing nutrient reduction in swine manure under aeration treatment since there was little difference found in terms of either nitrogen or phosphorus reduction between treatments with and without additives.